Ground Based Subsystems, For Inclusion In Optical Gateway, And That Interface With Optical Networks External To Optical Gateway

ABSTRACT

Described herein is a ground based subsystem for inclusion in an optical gateway and for use in transmitting an optical feeder uplink beam to a satellite. The subsystem can include a wavelength-division multiplexing (WDM) multiplexer configured to receive optical data signals from optical network(s) external to the ground based optical gateway, and configured to combine the optical data signals into a wavelength division multiplexed optical signal. The subsystem can also include an optical amplifier to amplify the wavelength division multiplexed optical signal, and transmitter optics to receive the amplified wavelength division multiplexed optical signal and transmit an optical feeder uplink beam to the satellite in dependence thereon. In certain embodiments, the ground based optical gateway does not perform any modulation or demodulation of the optical data signals received from the optical network(s) external to the ground based optical gateway before they are provided to the WDM multiplexer.

PRIORITY CLAIM

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/454,532, filed Feb. 3, 2017 (Attorney Docket No. SSLL-01037US0),which is incorporated by reference herein.

BACKGROUND

There is increasing need for large amounts of bandwidth to be routedbetween a ground based gateway and a spaced based satellite, as well asbetween space based satellites. With the recent announcement of plannedKa band and Ku band satellite constellations, it would be beneficial ifsuch frequency band satellite constellations can be used to help satisfythe aforementioned increasing need for large amounts of bandwidth to berouted between a ground based gateway and spaced based satellites, aswell as between space based satellites.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram describing a wireless communication system,which may be a satellite communication system.

FIG. 2A depicts gateway forward link equipment, according to anembodiment of the present technology.

FIG. 2B depicts components that can be used to produce data modulated RFcarriers introduced in FIG. 2A, according to an embodiment of thepresent technology.

FIG. 2C depicts components that can be used to produce data modulated RFcarriers introduced in FIG. 2A, according to another embodiment of thepresent technology.

FIG. 2D depicts one or more optical networks, which are external to thegateway forward link equipment introduced in FIG. 2A, providing opticalsignals to the gateway forward equipment.

FIG. 3 depicts space segment forward link equipment, according to anembodiment of the present technology.

FIGS. 4A and 4B depicts a portion of space segment return linkequipment, according to alternative embodiments of the presenttechnology.

FIG. 4C depicts a portion of space segment return link equipment,according to another embodiment of the present technology.

FIG. 4D depicts a further portion of space segment return linkequipment, according to an embodiment of the present technology.

FIG. 4E depicts a portion of space segment return link equipment,according to another embodiment of the present technology.

FIG. 5A depicts gateway return link equipment, according to anembodiment of the present technology.

FIG. 5B depicts gateway return link equipment, according to anotherembodiment of the present technology.

FIG. 6 is a high level flow diagram that is used to summarize methodsfor enabling a ground based subsystem to produce and transmit an opticalfeeder uplink beam to a satellite, according to certain embodiments ofthe present technology.

FIG. 7 is a high level flow diagram that is used to summarize methodsfor enabling a space based subsystem of a satellite to produce andtransmit a plurality of RF service downlink beams within a specified RFfrequency range to service terminals, according to certain embodimentsof the present technology.

FIG. 8 is a high level flow diagram that is used to summarize methodsfor enabling a space based subsystem of a satellite to produce andtransmit an optical feeder downlink beam, according to certainembodiments of the present technology.

FIG. 9A depicts space segment inter-satellite link (ISL) equipment andspace segment forward link equipment, according to an embodiment of thepresent technology.

FIG. 9B depicts space segment inter-satellite link (ISL) equipment andspace segment forward link equipment, according to another embodiment ofthe present technology.

FIG. 9C depicts space segment inter-satellite link (ISL) equipment,space segment forward link equipment, and space segment equipment thatcan consume one or more of the optical signals, according to anembodiment of the present technology.

FIG. 9D depicts space segment inter-satellite link (ISL) equipment,space segment forward link equipment, and space segment equipment thatcan consume one or more of the optical signals, according to anotherembodiment of the present technology.

FIG. 10A is a high level flow diagram that is used to summarize methodsfor enabling a space based subsystem to produce to an opticalinter-satellite link (ISL) beam and RF service downlink beams, based onan optical feeder uplink beam received from an optical gateway,according to an embodiment of the present technology.

FIG. 10B is a high level flow diagram that is used to summarize methodsfor enabling a space based subsystem to produce to an opticalinter-satellite link (ISL) beam and RF service downlink beams, based onan optical feeder uplink beam received from an optical gateway,according to another embodiment of the present technology.

FIG. 11A is a high level flow diagram that is used to summarize methodsfor enabling a space based subsystem to produce to an opticalinter-satellite link (ISL) beam and RF service downlink beams, based onan optical ISL beam received from another satellite, according to anembodiment of the present technology.

FIG. 11B is a high level flow diagram that is used to summarize methodsfor enabling a space based subsystem to produce to an opticalinter-satellite link (ISL) beam and RF service downlink beams, based onan optical ISL beam received from another satellite, according toanother embodiment of the present technology.

FIG. 12A depicts RF-to-optical space segment inter-satellite link (ISL)equipment, according to an embodiment of the present technology.

FIG. 12B depicts RF-to-optical space segment inter-satellite link (ISL)equipment, according to another embodiment of the present technology.

FIG. 12C depicts RF-to-optical space segment inter-satellite link (ISL)equipment, according to a further embodiment of the present technology.

FIG. 13A is a high level flow diagram that is used to summarize methodsfor enabling a space based subsystem to receive an RF feeder uplink beamand produce to an optical inter-satellite link (ISL) beam therefrom,according to an embodiment of the present technology.

FIG. 13B is a high level flow diagram that is used to summarize methodsfor enabling a space based subsystem to receive an RF feeder uplink beamand produce to two optical inter-satellite link (ISL) beams therefrom,according to an embodiment of the present technology.

DETAILED DESCRIPTION

Certain embodiments of the present technology described herein relate tosystem and subsystem architectures for high throughput satellites (HTS),very high throughput satellites (VHTS) and very very high throughputsatellites (VVHTS), which are also known as ultra high throughputsatellites (UHTS), all of which can be collectively referred to as HTS.Specific embodiments of the present technology described herein relateto space based subsystems that can receive optical feeder uplink beamsfrom a ground based gateway and in dependence thereon produce opticalinter-satellite link (ISL) beams and RF service downlink beams. Otherembodiments of the present technology described herein relate to spacebased subsystems that can receive modulated RF carriers from RF feederuplink beams from a ground based gateway and in dependence thereonproduce optical inter-satellite link (ISL) beams. An ISL beam mayadditionally or alternatively be produced by a spaced based subsystem(e.g., an ISL subsystem on a satellite) in dependence on one or moreservice uplink beams received from one or more service terminals STs. AnISL beam may additionally or alternatively be produced by a spaced basedsubsystem (e.g., an ISL subsystem on a satellite) in dependence on oneor more signals received from another subsystem (e.g., a non ISLsubsystem) on the satellite. Because of spectrum availability, if feederlinks between gateway (GW) sites and satellites are at opticalfrequencies, then the number of GW sites can be drastically reducedcompared to if the feeder links are at RF frequencies, which leads tosignificant cost savings in the space and ground segments.

Prior to describing details of specific embodiments of the presenttechnology, it is first useful to describe an exemplary wirelesscommunication system with which embodiments of the present technologywould be useful. An example of such a wireless communication system willnow be described with reference to FIG. 1.

FIG. 1 depicts a block diagram of a wireless communications system thatincludes a communication platform 100, which may be a satellite located,for example, at a geostationary or non-geostationary orbital location.Where a satellite is in a non-geostationary orbit, the satellite may bea low earth orbit (LEO) satellite. In other embodiments, other platformsmay be used such as an unmanned aerial vehicle (UAV) or balloon, or evena ship for submerged subscribers. In yet another embodiment, thesubscribers may be air vehicles and the platform may be a ship or atruck where the “uplink” and “downlink” in the following paragraphs arereversed in geometric relations. Platform 100 may be communicativelycoupled to at least one gateway (GW) 105 and a plurality of subscriberterminals ST (including subscriber terminals 107). The term subscriberterminals may be used to refer to a single subscriber terminal ormultiple subscriber terminals. A subscriber terminal ST is adapted forcommunication with the wireless communication platform 100, which asnoted above, may be a satellite. Subscriber terminals may include fixedand mobile subscriber terminals including, but not limited to, acellular telephone, a wireless handset, a wireless modem, a datatransceiver, a paging or position determination receiver, or mobileradio-telephone, or a headend of an isolated local network. A subscriberterminal may be hand-held, portable (including vehicle-mountedinstallations for cars, trucks, boats, trains, planes, etc.) or fixed asdesired. A subscriber terminal may be referred to as a wirelesscommunication device, a mobile station, a mobile wireless unit, a user,a subscriber, or a mobile. Where the communication platform of awireless communication system is a satellite, the wireless communicationsystem can be referred to more specifically as a satellite communicationsystem. For the remainder of this description, unless stated otherwise,it is assumed that the communication platform 100 is a satellite.Accordingly, platform 100 will often be referred to as satellite 100,and the wireless communication system will often be referred to as asatellite communication system. In accordance with certain embodiments,it is possible that a subscriber terminal with which one satellitewirelessly communicates is on a platform of or on another satellite.

In one embodiment, satellite 100 comprises a bus (e.g., spacecraft) andone or more payloads (e.g., the communication payload, an imagingpayload, etc.). The satellite will also include a command and datahandling system and multiple power sources, such as batteries, solarpanels, and one or more propulsion systems, for operating the bus andthe payload. The command and data handling system can be used, e.g., tocontrol aspects of a payload and/or a propulsion system, but is notlimited thereto.

The at least one gateway 105 may be coupled to a network 140 such as,for example, the Internet, terrestrial public switched telephonenetwork, mobile telephone network, or a private server network, etc.Gateway 105 and the satellite (or platform) 100 communicate over afeeder beam 102, which has both a feeder uplink 102 u and a feederdownlink 102 d. In one embodiment, feeder beam 102 is a spot beam toilluminate a region 104 on the Earth's surface (or another surface).Gateway 105 is located in region 104 and communicates with satellite 100via feeder beam 102. Although a single gateway is shown, someimplementations will include many gateways, such as five, ten, or more.One embodiment includes only one gateway. Each gateway may utilize itsown feeder beam, although more than one gateway can be positioned withina feeder beam. In one embodiment, a gateway is located in the same spotbeam as one or more subscriber terminals. In certain embodiments thefeeder uplink 102 u is an optical beam. In other embodiments the feederuplink 102 u is an RF beam. Similarly, it is possible that the feederdownlink 102 d is an optical beam or an RF beam, depending upon theembodiment.

Subscriber terminals ST and satellite 100 communicate over servicebeams, which are also known as user beams. For example, FIG. 1 showsservice beams 106, 110, 114 and 118 for illuminating regions 108, 112,116 and 120, respectively. In many embodiments, the communication systemwill include more than four service beams (e.g., sixty, one hundred,etc.). Each of the service beams have an uplink (106 u, 110 u, 114 u,118 u) and a downlink (106 d, 110 d, 114 d, 118 d) for communicationbetween subscriber terminals ST and satellite 100. Although FIG. 1 onlyshows two subscriber terminals within each region 108, 112, 116 and 120,a typical system may have thousands of subscriber terminals within eachregion. In the embodiments described herein, it is assumed that theservice beams (both downlink and uplink) are RF beams, as opposed tooptical beams.

In one embodiment, communication within the system of FIG. 1 follows anominal roundtrip direction whereby data is received by gateway 105 fromnetwork 140 (e.g., the Internet) and transmitted over the forward path101 to a set of subscriber terminals ST. In one example, communicationover the forward path 101 comprises transmitting the data from gateway105 to satellite 100 via uplink 102 u of feeder beam 102, through afirst signal path on satellite 100, and from satellite 100 to one ormore subscriber terminals ST via downlink 106d of service beam 106. Anuplink (e.g., 102 u) of a feeder beam (e.g., 102) can also be referredto more succinctly as a feeder uplink beam, and the downlink (e.g., 106d) of a service beam (e.g., a 106) can also be referred to moresuccinctly as a service downlink beam. Although the above examplementions service beam 106, the example could have used other servicebeams.

Data can also be sent from the subscriber terminals STs over the returnpath 103 to gateway 105. In one example, communication over the returnpath comprises transmitting the data from a subscriber terminal (e.g.,subscriber terminal 107 in service beam 106) to satellite 100 via uplink106 u of service beam 106, through a second signal path on satellite100, and from satellite 100 to gateway 105 via downlink 102 d of feederbeam 102. An uplink (e.g., 106 u) of a service beam (e.g., 106) can alsobe referred to more succinctly as a service uplink beam, and thedownlink 102 d of feeder beam 102 can also be referred to moresuccinctly as a feeder downlink beam. Although the above example usesservice beam 106, the example could have used any service beam.

FIG. 1 also shows that the satellite 100 can communicate with othersatellites 150 and 160 over respective inter-satellite link (ISL) beams152 and 162. For example, the satellite 100 can send data to thesatellite 150 over a path 153 of the ISL beam 152, and can receive datafrom the satellite 150 over a path 155 of the ISL beam 152.Communication over a forward path can comprise, for example,transmitting data from the gateway 105 to the satellite 100 via thefeeder uplink beam 102 u, through a signal path on satellite 100, andfrom the satellite 100 to the satellite 150 via the path 153 of the ISLbeam 152, through a signal path on the satellite 150, and then to one ormore subscriber terminals ST via a service downlink beam. Communicationover a return path can comprise, for example, transmitting data from asubscriber terminal to the satellite 150 via a service uplink beam,through a signal path on the satellite 150, and from the satellite 150to the satellite 100 via the path 155 of the ISL beam 152, and from thesatellite 100 to the gateway 105 via feeder downlink beam 102 d. Instill another example, the satellite 100 can receive data over a path163 of the ISL beam 162 from the satellite 160, and can send data over apath 153 of the ISL beam 152 to the satellite 150. These are just a fewexamples of how a ground based gateway can communicate with satellites,satellites can communicate with one another, and how satellites cancommunicate with service terminals STs, which examples not intended tobe all encompassing. All of the satellites 100, 150 and 160 shown inFIG. 1 can be in a geostationary orbit. Alternatively, all of thesatellites 100, 150 and 160 shown in FIG. 1 can be in anon-geostationary orbital, e.g., in a low earth orbit (LEO), and suchsatellites may only send an optical ISL beam from one satellite toanother when the other satellite comes into the view of the opticalcoverage area of the satellite. It is also possible that one or more ofthe satellites 100, 150 and 160 shown in FIG. 1 can be in ageostationary orbit, while one or more of the other satellites is withina non-geostationary orbital, e.g., in a low earth orbit (LEO). In thislatter case, a geostationary satellite and a non-geostationary satellite(e.g., an LEO satellite) may only be able to send an optical ISL beamtherebetween when one of the satellites comes into the view of theoptical coverage area of the other satellite. More generally, satellitesthat are in different types of orbits can send optical ISLs to oneanother using embodiments of the present technology described herein.This enables satellites to operate as optical repeaters without needingto demodulate and remodulate optical signals being forwarded to anothersatellite. Instead, a satellite that is acting as an optical repeatermay only need to amplify an optical ISL before it is passed onto anothersatellite, which can greatly simply the equipment onboard the satellite.

FIG. 1 also shows a Network Control Center (NCC) 130, which can includean antenna and modem for communicating with satellites 100, 150 and 160,as well as one or more processors and data storage units. NetworkControl Center 130 provides commands to control and operate satellites100, 150 and 160. Network Control Center 130 may also provide commandsto any of the gateways and/or subscriber terminals. It is also possiblethat the NCC includes transmitter and/or receiver optics for opticallycommunicating with satellites 100, 150 and 160 or communicates withsatellites 100, 150, and 160 through the optical gateway links such asbeam 102.

In one embodiment, communication platform 100 implements the technologydescribed below. In other embodiments, the technology described below isimplemented on a different platform (or different type of satellite) ina different communication system. For examples, the communicationplatform can alternatively be a UAV or balloon, but is not limitedthereto.

The architecture of FIG. 1 is provided by way of example and notlimitation. Embodiments of the disclosed technology may be practicedusing numerous alternative implementations.

Conventionally, a gateway (e.g., gateway 105) communicates with asatellite (e.g., satellite 100) using an antenna on the ground thattransmits and receives RF (radiofrequency) signals to and from anantenna on the satellite. Certain embodiments of the present technologyutilize optical components instead of antennas to transmit and receiveoptical signals between a gateway and a satellite or between satellites,as will be described in additional details below.

Certain embodiments of the present technology involve the use ofanalog-over free-space optical signals, which leads to an elegantarchitecture for a satellite repeater. Certain embodiments allow for theaggregation of multiple user links without requiring extra hardwareassociated with an onboard demodulator and remodulator, and thus reducethe mass, power and cost of the satellite, perhaps making the differencebetween being able to launch or not being able to launch the satellite.In addition, in accordance with specific embodiments where the uplinkand downlink communication signals are modulated at transmit (forward)and receive (return) RF frequencies, no frequency conversion in theforward link is required on the satellite, thereby further simplifyingthe payload design. By contrast, previously envisioned free-spaceoptical spacecraft architectures proposed demodulation of the opticalsignal, followed by routing to user link pathways and remodulation ofthe signal on user link RF frequencies.

Block diagrams for the communications subsystems for the ground andspace segments, according to certain embodiments of the presenttechnology, are described below with reference to FIGS. 2A, 3, 4A, 4B,4C, 4D and 5. Certain embodiments use analog modulation and demodulationon the satellite, thus enabling optical feeder links without onboardprocessing.

FIGS. 2A-2C will first be used to describe gateway forward linkequipment according to certain embodiments of the present technology.FIG. 3 will then be used to describe space segment forward linkequipment according to an embodiment of the present technology. Inspecific embodiments, 250 laser wavelengths are combined at a singlegateway (which can be referred to as an optical gateway) and sent to thesatellite, which has 500 user beams (also known as service beams)operating at Ka band frequencies. In accordance with an embodiment, eachwavelength carries 2.5 GHz so that a total of 625 GHz is sent from thegateway on the ground to the satellite. At a modest spectral efficiencyof 2 bps/Hz, this leads to a 1.25 Tb/s satellite design. In accordancewith another embodiment, each wavelength carries 2.9 GHz so that a totalof 725 GHz is sent from the gateway on the ground to the satellite. At amodest spectral efficiency of 2 bps/Hz, this leads to a 1.45 Tb/ssatellite design. FIGS. 4A-4C and 5 will thereafter be used to depictreturn link equipment for a satellite and a gateway.

Gateway Forward Link Equipment

FIG. 2A will now be used to describe gateway forward link equipment200A, according to an embodiment of the present technology. Such gatewayforward link equipment 200A can also be referred to as an opticalgateway forward link subsystem 200A, or more generally, as an opticalcommunication subsystem. Referring to FIG. 2A, the optical gatewayforward link subsystem 200A is shown as including two hundred and fiftylasers 202_1 to 202_250, two hundred and fifty electro-optical modulator(EOMs) 204_1 to 204_250, a wavelength-division multiplexing (WDM)multiplexer (MUX) 206, an optical amplifier (OA) 208 and transmitteroptics 210. Each of these elements are described below.

The two hundred and fifty separate lasers 202_1 to 202_250 each emitlight of a different wavelength within a specified wavelength range thatis for use in producing the optical feeder uplink beam (e.g., 102 u).The lasers can be referred to individually as a laser 202, orcollectively as the lasers 202. Where the specified wavelength range is,for example, from 1510 nanometers (nm) to 1560 nm, then the laser 202_1may emit light having a peak wavelength of 1510 nm, the laser 202_2 mayemit light having a peak wavelength of 1510.2 nm, the laser 202_3 (notshown) may emit light having a peak wavelength of 1510.4 nm, . . . thelaser 202_249 (not shown) may emit light having a peak wavelength of1559.8 nm, and the laser 202_250 may emit light having a peak wavelengthof 1660 nm. In other words, the peak wavelengths emitted by the lasers202 can occur at 0.2 nm intervals from 1510 nm to 1560 nm. Thewavelength range from 1510 nm to 1560 nm, which is within the infrared(IR) spectrum, is practical to use because IR lasers for use incommunications are readily available. However, wider or narrowwavelength ranges, within the same or other parts of the opticalspectrum, may alternatively be used. For example, it would also bepossible to utilize a wavelength range within the 400 nm-700 nm visiblespectrum. It is also possible that the wavelength range that isspecified for use in producing the optical feeder uplink beam (e.g., 102u) is non-contiguous. For example, the wavelength range that is for usein producing the optical feeder uplink beam can be from 1510 nm to1534.8 nm and from 1540.2 nm to 1564.8 m. Further, it is also possiblethat gateway forward link equipment can alternatively include more orless than two hundred and fifty lasers (that each emit light of adifferent peak wavelength within a specified contiguous ornon-contiguous wavelength range). Additionally, it is noted that thegateway forward link equipment may include two or more of each of thelasers (that each emit light of a different peak wavelength within aspecified contiguous or non-contiguous wavelength range) to provide forredundancy or backup. Each of the lasers 202 can be, for example, adiode-pumped infrared neodymium laser, although the use of other typesof lasers are also within the scope of the embodiments described herein.

To reduce and preferably avoid interference, the wavelength range thatis for use in producing the optical feeder uplink beam (e.g., 102 u)should be different than the wavelength range that is for use inproducing the optical feeder downlink beam (e.g., 102 d). For example,if the wavelength range that is for use in producing the optical feederuplink beam 102 u is from 1510 nm to 1560 nm, then the wavelength rangethat is for use in producing the optical feeder downlink beam 102 d canbe from 1560.2 nm to 1575 nm. For another example, if the wavelengthrange that is for use in producing the optical feeder uplink beam 102 uis from 1510 nm to 1534.8 nm and from 1540.2 nm to 1564.8 m, then thewavelength range that is for use in producing the optical feederdownlink beam 102 d can be from 1535 nm to 1540 nm and from 1565 nm to1575 nm.

These are just a few examples, which are not intended to be allencompassing. Details of how an optical feeder downlink beam (e.g., 102d) can be produced in accordance with an embodiment of the presenttechnology are provided below in the discussion of FIGS. 4A, 4B and 4C.

Still referring to FIG. 2A, the light emitted by each of the two hundredand fifty lasers 202, which can be referred to as an optical carriersignal, is provided (e.g., via a respective optical fiber) to arespective one of the two hundred and fifty separate EOMs 204_1 to204_250. The EOMs can be referred to individually as an EOM 204, orcollectively as the EOMs 204. Each of the EOMs is an optical device inwhich a signal-controlled element exhibiting an electro-optic effect isused to modulate a respective beam of light. The modulation performed bythe EOMs 204 may be imposed on the phase, frequency, amplitude, orpolarization of a beam of light, or any combination thereof. Inaccordance with a specific embodiment, each of the EOMs 204 is a phasemodulating EOM that is used as an amplitude modulator by using aMach-Zehnder interferometer. In other words, each of the EOMs 204 can beimplemented as a Mach-Zehnder modulator (MZM), which can be a LithiumNiobate Mach-Zehnder modulator, but is not limited thereto. Inaccordance with specific embodiments, each of the EOMs 204 isimplemented as an MZM that produces an amplitude modulated (AM) opticalwaveform with a modulation index between 10% and 80% in order tomaintain fidelity of an RF waveform (modulated therein) without too muchdistortion. The optical signal that is output by each of the EOMs 204can be referred to as an optical data signal. The modulation scheme thatis implemented by the EOMs 204 can result in double- orvestigial-sidebands, including both an upper sideband (USB) and a lowersideband (LSB). Alternatively single-sideband modulation (SSB) can beutilized to increase bandwidth and transmission power efficiency.

The two hundred and fifty separate optical data signals that are outputby the two hundred and fifty EOMs 204 are provided to the WDM MUX 206,which can also be referred to as a dense wavelength divisionmultiplexing (DWDM) MUX. The WMD MUX 206 multiplexes (i.e., combines)the two hundred and fifty optical data signals, received from the twohundred and fifty EOMs 204, onto a single optical fiber, with each ofthe two hundred and fifty separate optical data signals being carried atthe same time on its own separate optical wavelength within the rangefrom 1510 nm to 1560 nm. For example, as explained above, the twohundred and fifty separate optical data signals can have peakwavelengths of 1510 nm, 1510.2 nm, 1510.4 nm . . . 1559.8 nm and 1560nm. In accordance with certain embodiments, one or more of the opticalsignals that is/are provided to the WDM MUX 206 may come directly froman optical fiber of or attached to an optical network, such as, but notlimited to, a local area network (LAN), metropolitan area network (MAN)or wide area network (WAN).

The signal that is output by the WMD MUX 206, which can be referred toas a wavelength division multiplexed optical signal, is provided to theoptical amplifier (OA) 208. The OA 208 amplifies the wavelength divisionmultiplexed optical signal so that the wavelength division multiplexedoptical signal has sufficient power to enable transmission thereof fromthe ground to the satellite 100 in space. An exemplary type of OA 208that can be used is an erbium-doped fiber amplifier (EDFA). Howeverembodiments of the present technology are not limited to use with anEDFA. The output of the OA 208 can be referred to as an opticallyamplified wavelength division multiplexed optical signal.

The optically amplified wavelength division multiplexed optical signal,which is output by the OA 208, is provided (e.g., via an optical fiber)to the transmitter optics 210. The transmitter optics 210, which canalso be referred to as a telescope, can includes optical elements suchas lenses, mirrors, reflectors, filters and/or the like. The transmitteroptics 210 outputs a collimated optical feeder uplink beam that is aimedat a satellite. A gimbal, and/or the like, can be used to control thesteering of the transmitter optics 210. In accordance with anembodiment, the collimated optical feeder uplink beam has an aperture ofabout 100 cm, and a half beam divergence of about 0.0000004 radians,wherein the term “about” as used herein means +/−10 percent of aspecified value. The use of other apertures and half beam divergencevalues are also within the scope of the embodiments described herein.The collimated optical feeder uplink beam, which is output by thetransmitter optics 210, is transmitted in free-space to receiver opticson a satellite. The term “free-space” means air, outer space, vacuum, orsomething similar (which is in contrast to using solids such as opticalfiber cable, an optical waveguide or an optical transmission line).Reception and processing of the optical feeder uplink beam received atthe satellite will be described in additional detail below. However,before describing the reception and processing of the optical feederuplink beam received at the satellite, additional details of the gatewayforward link equipment, according to certain embodiments of the presenttechnology, will first be provided.

Referring again to the EOMs 204, in accordance with certain embodimentsof the present technology, each of the EOMs 204 modulates the opticalsignal it receives (e.g., via an optical fiber from a respective laser202) with a separate RF signal that has already been modulated toinclude user data. In order to eliminate the need for RF frequencydown-converters in the forward link equipment onboard the satellite, thecarrier frequencies of the RF signals that are used to modulate each ofthe two hundred and fifty lasers 202 on the ground (e.g., in gateway105) correspond to the desired user downlink frequency band within theKa band (or some other allotted band). As a result, the satelliterepeater is greatly simplified.

For example, a portion of the Ka band that may be desirable to use fortransmitting service downlink beams (also referred to as downlink userbeams) from satellite 100 to service terminals ST can be from 17.7-20.2GHz, and thus, includes a 2.5 GHz bandwidth. In such a case, each of theEOMs 204 could modulate the optical signal it receives (e.g., via anoptical fiber from a respective laser 202) with a separate RF signalhaving a frequency within the range from 17.7-20.2 GHz. Further, sinceeach of the two hundred and fifty optical data signals (produced by thetwo hundred and fifty EOMs) has a bandwidth of 2.5 GHz, the bandwidth ofthe optical feeder uplink beam that is sent from the ground to thesatellite is 625 GHz (i.e., 2.5 GHz*250=625 GHz).

For another example, a portion of the Ka band that may be desirable touse for transmitting service downlink beams (also referred to asdownlink user beams) from satellite 100 to service terminals ST can befrom 17.3-20.2 GHz, and thus, includes a 2.9 GHz bandwidth. In such acase, each of the EOMs 204 could modulate the optical signal it receives(e.g., via an optical fiber from a respective laser 202) with a separateRF signal having a frequency within the range from 17.3-20.2 GHz.Further, since each of the two hundred and fifty optical data signals(produced by the two hundred and fifty EOMs) has a bandwidth of 2.9 GHz,the bandwidth of the optical feeder uplink beam that is sent from theground to the satellite is 725 GHz (i.e., 2.9 GHz*250=725 GHz).

Where there is a desire or requirement that satellite 100 transmits fivehundred separate service downlink beams, then the portion of the opticalfeeder uplink beam that is produced by each of the two hundred and fiftylasers 202 needs to be modulated to carry the data for two of the fivehundred service downlink beams. In other words, each of the opticalsignals produced by each of the two hundred and fifty lasers 202 needsto be modulated to carry the data for two of the five hundred servicedownlink beams. This can be achieved by using half of the availableportion of the Ka band for carrying the data for one service downlinkbeam, and the other half of the available portion of the Ka band forcarrying the data for another service downlink beam. For example, wherethe portion of the Ka band that is available for transmitting servicedownlink beams (also referred to as downlink user beams) is from17.7-20.2 GHz, then 17.7-18.95 GHz can be used for carrying the data forone service downlink beam, and 18.95-20.2 GHz can be used for carryingthe data for another service downlink beam. For another example, wherethe portion of the Ka band that is available for transmitting servicedownlink beams (also referred to as downlink user beams) is from17.3-20.2 GHz, then 17.3-18.75 GHz can be used for carrying the data forone service downlink beam, and 18.75-20.2 GHz can be used for carryingthe data for another service downlink beam.

FIG. 2B depicts components that can be used to produce one of the datamodulated RF carriers introduced in FIG. 2A, according to an embodimentof the present technology. The components shown in FIG. 2B would beuseful where each of the optical data signals produced by each of theEOMs 204 carries the data for one service downlink beam (e.g., for oneof the two hundred and fifty service downlink beams). Referring to FIG.2B, shown therein is a local oscillator (LO) 222 that produces an RFcarrier signal within the portion of the Ka band that is available fortransmitting service downlink beams (also referred to as downlink userbeams). For example, the LO 222 may produce an RF carrier within the RFfrequency range from 17.7-20.2 GHz (e.g., at 18.95 GHz, but not limitedthereto). For another example, the LO 222 may produce an RF carrierwithin the RF frequency range from 17.3-20.2 GHz (e.g., at 18.75 GHz,but not limited thereto). The RF carrier signal that is output by the LO222 is provided to an RF modulator (RFM) 224, which also receives a datasignal. The RFM 224 modulates that data signal onto the RF carriersignal to produce a data modulated RF carrier signal, which is providedto one of the EOMs 204 shown in FIG. 2A. Where two hundred and fiftydata modulated RF carrier signals are produced (each of which isprovided to a different one of the EOMs 204), the components shown inFIG. 2B can be duplicated two hundred and fifty times. Alternatively,the two hundred and fifty RFMs 224 can receive the same carrier signalfrom a common LO 222, with each of the RFMs 224 receiving a separatedata signal.

FIG. 2C depicts components that can be used to produce one of the datamodulated RF carriers introduced in FIG. 2A, according to an alternativeembodiment of the present technology. The components shown in FIG. 2Cwould be useful where each of the optical data signals produced by eachof the EOMs 204 carries the data for two of the service downlink beams(e.g., for two of the five hundred service downlink beams). Referring toFIG. 2C, shown therein is a first LO 222_1 and a second LO 222_2, afirst RFM 224_1 and a second RFM 224_2, and a frequency divisionmultiplexer (FDM) 226. The LO 222_1 and the LO 222_2 each produces adifferent RF carrier signal within the portion of the Ka band that isavailable for transmitting service downlink beams (also referred to asdownlink user beams). For example, the LO 222_1 may produce an RFcarrier within the RF frequency range from 17.7-18.95 GHz (e.g., at18.325 GHz, but not limited thereto), and the LO 222_2 may produce an RFcarrier within the RF frequency range from 18.95-20.2 GHz (e.g., at19.575, but not limited thereto). For another example, the LO 222_1 mayproduce an RF carrier within the RF frequency range from 17.3-18.75 GHz(e.g., at 18.025 GHz, but not limited thereto), and the LO 222_2 mayproduce an RF carrier within the RF frequency range from 18.75-20.2 GHz(e.g., at 19.475, but not limited thereto). The RFM 224_1 modulates afirst data signal onto the RF carrier signal produced by the LO 222_1 tothereby produce a first data modulated RF carrier signal. The RFM 224_2modulates a second data signal onto the RF carrier signal produced bythe LO 222_2 to thereby produce a second data modulated RF carriersignal. The first and second data modulated RF carrier signals, whichare produced by the RFMs 224_1 and 224_2, are provided to the FDM 226.The FDM 226 frequency multiplexes the first and second data modulated RFcarrier signals, received from the two RFMs 224_1 and 224_2, onto asingle carrier medium (e.g., cable, wire or trace), with each of the twodata modulated RF carrier signals being carried at the same time at itsown separate frequency sub-band. The output of the FDM 226 is providedto one of the EOMs 204 shown in FIG. 2A. Where two hundred and fiftydata modulated RF carrier signals are produced (each of which isprovided to a different one of the EOMs 204), the components shown inFIG. 2C can be duplicated two hundred and fifty times. Alternatively,two hundred and fifty of the RFMs 224 can receive the same carriersignal from a common LO 222_1, and another two hundred and fifty RFMs224 can receive the same carrier signal from a common LO 222_2, witheach of the RFMs 224 receiving a separate data signal. Other variationsare also possible, and within the scope of an embodiment of the presenttechnology.

The RFMs 224 can perform various different types of RF modulation,depending upon implementation and other factors such channel conditions.For example, the RFMs 224 can perform Amplitude-shift keying (ASK),Phase-shift keying (PSK), or Amplitude and phase-shift keying (APSK)types of modulation (e.g., 16-, 128-or 256-APSK), just to name a few. Inaccordance with certain embodiments, the modulation scheme performed bythe RFMs 224 and EOMs 204 cause the signals that are transmitted fromthe ground to a satellite to be in conformance with the Digital VideoBroadcasting-Satellite-Second Generation (DVB-S2) standard, or therelated DVB-S2X standard (which is an extension of the DVB-S2 standard).

Referring again to FIG. 2A, in order to wavelength division multiplextwo hundred and fifty wavelengths produced by the two hundred and fiftylasers 202_1 to 202_250, a combination of C band optical frequencies(from 1530 m to 1565 nm) and L band optical frequencies (from 1565 nm to1625 nm) may be used, in order to keep the separation of the wavelengthsto be at least 20-25 GHz in order to reduce and preferably minimizeinter-wavelength interference that may occur in an optical fiber due tonon-linearities. If fewer wavelengths are used (e.g., at C band alone),and higher bandwidth is available at Ka band per user beam (e.g., if 2.9GHz is available as it is in certain ITU Regions), the overallthroughput still remains of the order of several hundred GHz, which letsthe capacity reach the Tb/s range. If instead each wavelength carriesmore than the Ka band user bandwidth, fewer wavelengths can be used, butsome amount of frequency conversion would be needed in the space segmentforward link equipment.

A data modulated RF carrier signal (including data for one servicedownlink beam) can be provided to one EOM 204, and the optical datasignal output from that EOM 204 (and provided to the WDM MUX 206) caninclude data for the one service downlink beam, as can be appreciatedfrom FIGS. 2A and 2B. Alternatively, two data modulated RF carriersignals (including data for two service downlink beams) can be providedto the same EOM 204, and the optical data signal output from that EOM204 (and provided to the WDM MUX 206) can include data for the twoservice downlink beams, as can be appreciated from FIGS. 2A and 2C. Instill other embodiments, two or more data modulated RF carrier signals(including data for the same service downlink beam) can be provided toone EOM 204, and the optical data signal output from the EOM 204 (andprovided to the WDM MUX 206) can include data (of the two or more datamodulated RF carrier signals) to be included in the one service downlinkbeam. Other variations are also possible, and within the scope of theembodiments disclosed herein.

As noted above, in accordance with certain embodiments, one or more ofthe optical signals that is/are provided to the WDM MUX 206 may comefrom an optical fiber of or attached to an optical network, such as, butnot limited to, a local area network (LAN), metropolitan area network(MAN) or wide area network (WAN). Such an optical network can beexternal to the gateway in which the gateway forward link equipment islocated. An example of such an embodiment is shown in FIG. 2D. Morespecifically, FIG. 2D depicts one or more optical networks, which areexternal to the gateway that includes gateway forward link equipment200D, providing optical signals to the gateway forward equipment 200D sothat the data included in the optical signals (received from theexternal optical networks) can be included in the optical feeder uplinkbeam that is transmitted from the gateway through free-space to asatellite. Although not specifically shown in FIG. 2D, each opticalsignal path that provides an optical signal from an optical networkexternal to the gateway to the WDM MUX 206 may include a filter toremove unwanted frequencies and/or an optical amplifier (OA) to amplifythe signal before it is provided to the WDM MUX 206. Exemplary detailsof such filters and OAs have been described herein, and thus, need notbe repeated. Since each of the optical signals provided to the WDM MUX206 should have a different optical wavelength, to enable wavelengthdivisional multiplexing to be performed, the optical signal receivedfrom the external optical networks should have an appropriate opticalwavelength that differs from other wavelengths being provided to the WDMMUX 206, or alternatively, can be converted to an appropriate opticalwavelength that differs from other wavelengths being provided to the WDMMUX 206. One or more optical wavelength converters, within or externalto the optical gateway, can be used to perform such wavelengthconversions. The embodiments described with reference to FIG. 2D (aswell as FIG. 5B, discussed below) can provide enhanced end-to-endsecurity, e.g., for military and/or other government data, because thegateway does not need any knowledge of the modulation and/or encryptionschemes used on the optical signals that are being received from and/orforwarded to the optical network(s) that is/are external to the opticalgateway.

In accordance with certain embodiments, the gateway forward linkequipment 200D can optionally include wavelength converters 232, whereineach of the wavelength converters 232 is configured to convert a peakoptical wavelength of one of the one or more optical data signals,received from the one or more optical networks that are external to theground based optical gateway (that includes the gateway forward linkequipment 200D), to a different peak optical wavelength so that no twooptical signals received at different inputs of the WDM multiplexer 206have a same peak optical wavelength. Additionally, or alternatively, thegateway forward link equipment 200D can optionally include one or morefrequency converters 234, wherein each of the frequency converters 234is configured to up-convert or down-convert a frequency of a differentone of the optical signals being provided to the WDM multiplexer 206(from one of the one or more optical networks that are external to theground based optical gateway that includes the gateway forward linkequipment 200D), to thereby eliminate any need for frequency conversionto be performed on the satellite to which the optical feeder uplink beamis being transmitted. Wavelength conversion can be performed prior tothe frequency conversion, as shown in FIG. 2D, or alternatively,frequency conversion can be performed prior to the wavelengthconversion. For example, the relative positions of the wavelengthconverters 232 and the frequency converters 234 in FIG. 2D can beswapped.

Referring again to FIG. 2C, it is also possible that an FDM 226 receivesmore two data modulated RF carrier signals, e.g., from more than twoRFMs 224. This can enable, among other things, one service downlink beamto include more than two data modulated RF carriers.

Space Segment Forward Link Equipment

FIG. 3 will now be used to describe space segment forward link equipment300 according to an embodiment of the present technology. Such spacesegment forward link equipment 300, which can also be referred to as aforward link satellite subsystem 300, or more generally, as an opticalcommunication subsystem, is configured to receive the optical signalthat is transmitted from the ground based optical gateway subsystem 200Aor 200D to the satellite that is carrying the space segment forward linkequipment 300. The space segment forward link equipment 300 is alsoconfigured to convert the optical signal that it receives (from theground based optical gateway subsystem 200A or 200D) into electricalsignals, and to produce service beams therefrom, wherein the servicebeams are for transmission from the satellite to service terminals STs.

Referring to FIG. 3, the forward link satellite subsystem 300 is shownas including receiver optics 302, an optical amplifier (OA) 304, awavelength-division multiplexing (WDM) demultiplexer (DEMUX) 306, twohundred and fifty photodetectors (PDs) 308_1 to 308_250, two hundred andfifty filters 310_1 to 310_250, two hundred and fifty low noiseamplifiers (LNAs) 312_1 to 312_250, and two hundred and fifty splitters314_1 to 314_250. The forward link satellite subsystem 300 is also shownas including five hundred filters 316_1 to 316_500, high poweramplifiers (HPAs) 318_1 to 318_500, harmonic filters (HFs) 320_1 to320_500, test couplers (TCs) 322_1 to 322_500, orthomode junctions(OMJs) 324_1 to 324_500, and feed horns 326_1 to 326_500. The PDs 308_1to 308_250 can be referred to individually as a PD 308, or collectivelyas the PDs 308. The filters 310_1 to 310 250 can be referred toindividually as a filter 310, or collectively as the filters 310. TheLNAs 312_1 to 312_250 can be referred to individually as an LNA 312, orcollectively as the LNAs 312. The filters 316_1 to 316_500 can bereferred to individually as a filter 316, or collectively as the filters316. The HPAs 318_1 to 318_500 can be referred to individually as an HPA318, or collectively as the HPAs 318. The HFs 320_1 to 320_500 can bereferred to individually as an HF 320, or collectively as the HFs 320.The TCs 322_1 to 322_500 can be referred to individually as a TC 322, orcollectively as the TCs 322. The OMJs 324_1 to 324_500 can be referredto individually as an OMJ 324, or collectively as the OMJs 324. The feedhorns 326_1 to 326_500 can be referred to individually as a feed horn326, or collectively as the feed horns 326.

The receiver optics 302, which can also be referred to as a telescope,can includes optical elements such as mirrors, reflectors, filtersand/or the like. The receiver optics 302 receives the optical feederuplink beam that is transmitted through free-space to the satellite bythe ground based optical gateway forward link subsystem 200A or 200D,and provides the received optical feeder uplink beam (e.g., via anoptical fiber) to the OA 304. A gimbal, and/or the like, can be used tocontrol the steering of the receiver optics 302. When the optical feederuplink beam reaches the satellite, the power of the optical feederuplink beam is significantly attenuated compared to when it wastransmitted by the ground based optical gateway subsystem 200A or 200D.Accordingly, the OA 304 is used to amplify the received optical feederuplink beam before it is provided to the WDM DEMUX 306. The OA 304 canbe, e.g., an erbium-doped fiber amplifier (EDFA), but is not limitedthereto. The output of the OA 304 can be referred to as an opticallyamplified received optical feeder uplink beam. The WDM DEMUX 306demultiplexes (i.e., separates) the received optical feeder uplink beam(after it has been optically amplified) into two hundred and fiftyseparate optical signals, each of which is provided to a separatephotodetector (PD) 308. Each PD 308 converts the optical signal itreceives from the WDM DEMUX 306 to a respective RF electrical signal.The RF electrical signal produced by each PD 308 is provided to arespective filter (FTR) 310 (e.g., a bandpass filter) to remove unwantedfrequency components and/or enhance desired frequency components. For anexample, each filter 310 can pass frequencies within the range of17.7-20.2 GHz, or within the range of 17.3-20.2 GHz, but are not limitedthereto. The filtered RF electrical signal, which is output by eachfilter 310, is provided to a respective low noise amplifier (LNA) 312.Each LNA 312 amplifies the relatively low-power RF signal it receivesfrom a respective filter 310 without significantly degrading the signalssignal-to-noise ratio. The amplified RF signal that is output by eachLNA 312 is provided to an optional respective splitter 314.

The splitter 314 splits the amplified RF signal it receives into twocopies, each of which has half the power of the amplified RF signal thatis provided to the input of the splitter 314. Each splitter 314 can beimplemented by a hybrid, but is not limited thereto. In accordance withcertain embodiments of the present technology, one of the RF signalsthat is output by a splitter 314 is used to produce one service beam,and the other RF signal that is output by the same splitter 314 is usedto produce another service beam. Each of the copies of the RF signalthat is output by the splitter 314 is provided to a respective filter316. For example, the splitter 314_1 provides one copy of the RF signalit receives to the filter 316_1, and provides another copy of the RFsignal it receives to the filter 316_2. In accordance with certainembodiments, the pair of filters 316 that receive RF signals from thesame splitter 314 have pass bands that differ from one another. Forexample, the filter 316_1 may have a passband of 17.7-18.95 GHz and thefilter 316_2 may have a passband of 18.95-20.2 GHz. For another example,the filter 316 1 may have a passband of 17.3-18.75 GHz and the filter316_2 may have a passband of 18.75-20.2 GHz. This enables each splitter314 and pair of filters 316, which are fed by the splitter 314, toseparate a signal received by the splitter into two separate RF signalscorresponding to two separate user beams. The use of other passbands arepossible and within the scope of an embodiment of the presenttechnology.

Each HPA 318 amplifies the RF signal it receives so that the RF signalhas sufficient power to enable transmission thereof from the satellite100 in space to an ST, which may be on the ground. Each HPA 318 can be,e.g., a liner traveling wave tube high power amplifier, but is notlimited thereto. The signal that is output by each of the HPAs 318 canbe referred to as an amplified RF signal. Each HF 320 is used to reduceand preferably remove any distortion in the amplified RF signal that wascaused by a respective HPA 318. Each HF 320 can be, e.g., an RLC circuitbuilt from resistive (R), inductive (L) and capacitive (C) elements, butis not limited thereto.

Each test coupler TC 322 can be used for power monitoring, payloadtesting and/or performing calibrations based on signals passingtherethrough. Each OMJ 324 adds either right hand circular polarization(RHCP) or left hand circular polarization (LHCP) to the RF signal thatis passed through the OMJ. This allows for color reuse frequency bandallocation, wherein each color represents a unique combination of afrequency band and an antenna polarization. This way a pair of feederbeams that illuminate adjacent regions can utilize a same RF frequencyband, so long as they have orthogonal polarizations. Alternatively, eachOMJ 324 adds either horizontal linear polarization or vertical linearpolarization to the RF signal that is passed through the OMJ. Each feedhorn 326 converts the RF signal it receives, from a respective OMJ 324,to radio waves and feeds them to the rest of the antenna system (notshown) to focus the signal into a service downlink beam. A feed horn 326and the rest of an antenna can be collectively referred to as theantenna. In other words, an antenna, as the term is used herein, caninclude a feed horn. All or some of the feed horns 326 can share acommon reflector. Such reflector(s) is/are not shown in the Figures, tosimply the Figures.

Space Segment Return Link Equipment

FIG. 4A will now be used to describe a portion of space segment returnlink equipment 400A, according to an embodiment of the presenttechnology. Such space segment return link equipment 400A, which canalso be referred to as a satellite return link subsystem 400A, or moregenerally, as an optical communication subsystem, is configured toreceive the RF signals that are transmitted by service terminals STs tothe satellite (e.g., 100) that is carrying the space segment return linkequipment 400A. The space segment return link equipment 400A, togetherwith the space segment return link equipment 400D in FIG. 4D, is alsoconfigured to convert the RF signals that it receives (from the serviceterminals STs) into optical signals, and to produce optical returnfeeder beams, wherein the optical return feeder beams are fortransmission from the satellite (e.g., 100) to a ground based gateway(e.g., 105).

Referring to FIG. 4A, the portion of the space segment return linkequipment 400A shown therein includes feed horns 402_1 to 402_500 (whichcan be referred to individually as a feed horn 402, or collectively asthe feed horns 402), orthomode junctions (OMJs) 404 1 to 404_500 (whichcan be referred to individually as an OMJ 404, or collectively as theOMJs 404), test couplers (TCs) 406_1 to 406_500 (which can be referredto individually as a TC 406, or collectively as the TCs 406), pre-selectfilters (PFs) 408_1 to 408_500 (which can be referred to individually asa PF 408, or collectively as the PFs 408), low noise amplifiers (LNAs)410_1 to 410_500 (which can be referred to individually as an LNA 410,or collectively as the LNAs 410), and filters 412_1 to 412_500 (whichcan be referred to individually as a filter 412, or collectively as thefilters 412). The portion of the space segment return link equipment400A shown in FIG. 4A also includes optional combiners 414_1 to 414_250(which can be referred to individually as a combiner 414, orcollectively as the combiners 414), frequency down-converters 416_1 to416_250 (which can be referred to individually as a frequencydown-converter 416, or collectively as the frequency down-converters416), filters 418_1 to 418_250 (which can be referred to individually asa filter 418, or collectively as the filters 418), and local oscillators(LOs) 422_1 to 422_4 (which can be referred to individually as an LO422, or collectively as the LOs 422). The portion of the space segmentreturn link equipment 400A shown in FIG. 4A also includes combiners420_1 to 420_125 (which can be referred to individually as a combiner420, or collectively as the combiners 420).

Each feed horn 402 gathers and focuses radio waves of a service uplinkbeam (e.g., 106 u) and converts them to an RF signal that is provided toa respective OMJ 404. A feed horn 402 and the rest of an antenna can becollectively referred to as the antenna or antenna system. In otherwords, an antenna, as the term is used herein, can include a feed horn.All or some of the feed horns 402 can share a common reflector. Suchreflector(s) is/are not shown in the Figures, to simply the Figures.Each OMJ 404 either passes through a right hand circular polarization(RHCP) or a left hand circular polarization (LHCP) RF signal. Each OMJ404 can alternatively pass through either a horizontal or a verticallinear polarization RF signal. Each test coupler TC 406 can be used forpower monitoring, payload testing and/or performing calibrations basedon signals passing therethrough. Each pre-select filter (PF) 408 (e.g.,a bandpass filter) is used to remove unwanted frequency componentsand/or enhance desired frequency components. For an example, each PF 408can pass frequencies within the range of 29.5-30.0 GHz, but is notlimited thereto. Each LNA 410 amplifies the relatively low-power RFsignal it receives from a respective PF 408 without significantlydegrading the signals signal-to-noise ratio. The amplified RF signalthat is output by each LNA 410 is provided to a respective filter 412.

Each filter 412 allows frequencies to pass within one of the colors a,b, c or d. For example, the filter 412_1 passes frequencies within thecolor a, the filter 412_2 passes the frequencies within the color b, thefilter 412_3 passes frequencies within the color c, and the filter 412_4passes frequencies within the color d. In accordance with an embodiment:color ‘a’ represents a first sub-band (e.g., 29.50-29.75 GHz) of anallocated uplink frequency band (e.g., 29.50-30.00 GHz) with aright-hand circular polarization (RHCP); color ‘b’ represents a secondsub-band (29.75-30.00 GHz) of the allocated uplink frequency band withRHCP; color ‘c’ represents the first sub-band (e.g., 29.50-29.75 GHz) ofthe allocated uplink frequency band with a left-hand circularpolarization (LHCP); and color ‘d’ represents the second sub-band(29.75-30.00 GHz) of the allocated uplink frequency band with LHCP. Inother embodiments, the colors may include other allocations of thefrequency band and polarization.

Each pair of the filters 412 provide their outputs to a combiner 414.For example, the filters 412_1 and 412_2 provide their outputs to thecombiner 414_1, and the filters 414_3 and 414_4 provide their outputs tothe combiner 414_2. Each optional combiner 414 functions as adirectional coupler that combines two RF signals into one. For example,the combiner 414_1 combines RF signal having the color a (received fromthe filter 412_1) and the RF signal having the color b (received fromthe filter 412_2) into a single RF signal that is provided to thefrequency down-converter 416_1. Similarly, the combiner 414_3 combinesRF signal having the color c (received from the filter 412_3) and the RFsignal having the color d (received from the filter 412_4) into a singleRF signal that is provided to the frequency down-converter 416_2. Eachcombiner 414 can be implemented by a hybrid, but is not limited thereto.

Each frequency down-converter 416 receives an RF signal from a combiner414 (which RF signal includes data from two service uplink beams, andthus, can be referred to as an RF data signal) and an RF signal from anLO 422 (which can be referred to as an LO signal), and uses the LOsignal to down-convert the RF data signal to a frequency range (e.g.,6.70-7.2 GHz, or 6.3-7.2 GHz, or some other frequency range within the6-12 GHz band) that can be used for transmitting feeder downlink signals(e.g., 102 d) to a gateway (e.g., 105). The output of each frequencydown-converter 416 is provided to a filter 418. For example, thefrequency down-converter 416_1 provides its output to the A,B filter418_1, and the frequency down-converter 416_1 provides its output to theC,D filter 418_2. The A,B filter 418_1 is a bandpass filter that allowsfrequencies to pass within the bands associated with colors A and B. TheC,D filter 418_2 is a bandpass filter that allows frequencies to passwithin the bands associated with colors C and D. In accordance with anembodiment: color ‘A’ represents a first sub-band (e.g., 6.7-6.95 GHz)of an allocated downlink frequency band (e.g., 6.7-7.2 GHz) withright-hand circular polarization (RHCP); color ‘B’ represents a secondsub-band (e.g., 6.95-7.2 GHz) of the allocated downlink frequency bandwith RHCP; color ‘C’ represents the first sub-band (e.g., 6.7-7.95 GHz)of the allocated downlink frequency band with a left-hand circularpolarization (LHCP); and color ‘D’ represents the second sub-band (e.g.,6.95-7.2 GHz) of the allocated uplink frequency band with LHCP. Foranother example: color ‘A’ represents a first sub-band (e.g., 6.3-6.75GHz) of an allocated downlink frequency band (e.g., 6.3-7.2 GHz) withright-hand circular polarization (RHCP); color ‘B’ represents a secondsub-band (e.g., 6.75-7.2 GHz) of the allocated downlink frequency bandwith RHCP; color ‘C’ represents the first sub-band (e.g., 6.3-7.75 GHz)of the allocated downlink frequency band with a left-hand circularpolarization (LHCP); and color ‘D’ represents the second sub-band (e.g.,6.75-7.2 GHz) of the allocated uplink frequency band with LHCP. In otherembodiments, the colors may include other allocations of a frequencyband and polarization.

In the embodiment of FIG. 4A, the outputs of four filters 418 areprovided to a combiner 420. For example, the outputs of filters 418_1,418_2, 418_3 and 418_4 are provided the combiner 420_1. Each combiner420 combines the four down-converted and filtered signals it receivesinto a combined signal that includes data modulated RF carriers foreight service uplink beams. In other words, the output of each combiner420 includes data received from eight service uplink beams associatedwith at least eight service terminals STs. The output of each combiner420 is provided to a separate EOM 434, as will be discussed below withreference to FIG. 4D. However, prior to discussing FIG. 4D, FIGS. 4B and4C will first be used to describe alternative ways in which datamodulated RF carriers are produced from multiple (e.g., eight) serviceuplink beams.

FIG. 4B depicts a portion of space segment return link equipment 400B,according to an embodiment of the present technology. FIG. 4B is similarto FIG. 4A, except that instead of combining the outputs of four filters418 using a single combiner 420, the outputs of two filters 418 arecombined into one signal using a combiner 421, and the outputs of twocombiners 421 are combined using a combiner 423. For example, theoutputs of filters 418_1, 418_2 are combined using the combiner 421_1,and the outputs of filter 418_3 and 418_4 are combined by the combiner421_2, and the outputs of the combiners 421_1 and 421_2 are combined bythe combiner 423_1. Similar to the case in FIG. 4A, the output of thecombiner 423_1 is a combined signal that includes data modulated RFcarriers for eight service uplink beams. In other words, the output ofeach combiner 420 includes data for eight service uplink beamsassociated with multiple (e.g., eight) service terminals STs. The outputof each combiner 423 is provided to a separate EOM 434, as will bediscussed below with reference to FIG. 4D.

In the embodiments shown and described with reference to FIGS. 4A and4B, the frequency down-converters 416 were shown and described as beingused to perform frequency conversions within the space segment returnlink equipment 400A and 400B. In alternative embodiments of the presenttechnology, the frequency down-converters 416 (and the filters 418) areeliminated, in which case the space segment return link equipment 400Aand 400B perform no frequency conversions thereby simplifying the spacesegment return link equipment. In such alternative embodiments, theoutputs of the combiners 414 can be provided directly to the combiners420 (in FIG. 4A) or the combiners 421 (in FIG. 4B). Such alternativeembodiments, which eliminate frequency conversion on the return link,provide for less bandwidth on the return link than the embodiments ofFIGS. 4A and 4B. Less bandwidth on the return link should typically beacceptable, since a return link typically needs to handle much lessbandwidth than a forward link since service terminals STs typicallydownload much more data than they upload. An example of such analternative embodiment, is shown in FIG. 4C. In the embodiment of FIG.4C, the outputs of two of the filters 412 are provided to a combiner414, and the outputs of four of the combiners 414 is provided to acombiner 420. In another embodiment, the outputs of eight of the filters412 (e.g., the filters 412_1 to 412_8) are all provided directly to asame combiner (e.g., the combiner 420_1). In other words, there can beless cascading of combiners. In still another embodiment, there can beadditional cascading of combiners, e.g., in a similar manner as wasshown in FIG. 4B.

FIGS. 4A, 4B and 4C were used to described portions of space segmentreturn link equipment (400A or 400B) that produce a data modulated RFcarrier for multiple (e.g., eight) service uplink beams associate withmultiple (e.g., eight or more) service terminals STs. FIG. 4D will nowbe used to describe a further portion of the space segment return linkequipment 400D that is used to convert the data modulated RF carriersignals into a collimated optical downlink feeder beam that is aimed ata gateway. Referring to FIG. 4D, the portion of the space segment returnlink equipment 400D is shown as including sixty three lasers 432_1 to432_63, sixty three electro-optical modulator (EOMs) 434_1 to 434_63, awavelength-division multiplexing (WDM) multiplexer (MUX) 436, an opticalamplifier (OA) 438 and transmitter optics 440. Each of these elementsare described below.

The sixty three separate lasers 432_1 to 432_63 each emit light of adifferent wavelength within a specified wavelength range. The lasers canbe referred to individually as a laser 432, or collectively as thelasers 432. Where the specified wavelength range is, for example, from1560.2 nm to 1575 nm, then the laser 432_1 may emit light having a peakwavelength of 1560.2 nm, the laser 432_2 may emit light having a peakwavelength of 1560.4 nm, the laser 432_3 (not shown) may emit lighthaving a peak wavelength of 1560.6 nm, . . . the laser 432_62 may emitlight having a peak wavelength of 1672.6 nm, and the laser 432_63 mayemit light having a peak wavelength of 1672.8 nm. In other words, thepeak wavelengths emitted by the lasers 432 can occur at 0.2 nm intervalsfrom 1560.2 nm to 1572.8 nm. The wavelength range from 1560.2 nm to 1575nm, which is within the IR spectrum, is practical to use because IRlasers for use in communications are readily available. However, wideror narrow wavelength ranges, within the same or other parts of theoptical spectrum, may alternatively be used. For example, it would alsobe possible to utilize a wavelength range within the 400 nm-700 nmvisible spectrum. It is also possible that the wavelength range that isspecified for use in producing the optical feeder downlink beam (e.g.,102 d) is non-contiguous. For example, the wavelength range that is foruse in producing the optical feeder downlink beam can be from 1535 nm to1540 nm and from 1565 nm to 1575 nm. These are just a few examples,which are not intended to be all encompassing. Further, it is alsopossible that space segment return link equipment can alternativelyinclude more or less than sixty three lasers (that each emit light of adifferent peak wavelength within a specified contiguous ornon-contiguous wavelength range). Additionally, it is noted that thespace segment return link equipment may include two or more of each ofthe lasers (that each emit light of a different peak wavelength within aspecified contiguous or non-contiguous wavelength range) to provide forredundancy or backup. Each of the lasers 432 can be, for example, adiode-pumped infrared neodymium laser, although the use of other typesof lasers are also within the scope of the embodiments described herein.

In accordance with certain embodiments, the space segment return linkequipment 400D includes less lasers (e.g., sixty three lasers 432) foruse in generating the optical feeder downlink beam that is aimed fromthe satellite 100 to the gateway 105, than the gateway forward linkequipment 200A or 200D includes (e.g., five hundred lasers 202) forgenerating the optical feeder uplink beam that is aimed from the gateway105 to the satellite 100. This is made possible due to currentasymmetric capacity requirements between the forward and return feederlinks. More specifically, a feeder downlink beam (e.g., 102 d) carriessignificantly less data than a feeder uplink beam (e.g., 102 u), becauseservice terminals STs typically download much more data than theyupload.

On the return link, given the current asymmetric capacity requirementsbetween the forward and return links, the space segment return linkequipment can be implemented to handle less demand that the ground basedforward link equipment. As an example, if each RF service uplink beam isassumed to have only 320 MHz per beam, then a total of 160 GHz needs tobe sent from a satellite to a gateway on the optical feeder downlinkbeam. Several beams' frequencies can be grouped together to create a 4GHz bandwidth which is then transmitted on each of sixty three laserwavelengths that are multiplexed together and transmitted to the ground.An alternative implementation would be to aggregate the 4 GHz spectrumwith filtering post LNA to eliminate the RF frequency conversion and asabove directly modulate the RF spectrum on each of the sixty three laserwavelengths. An alternative implementation would be to use only RF LNAsfor each feed, modulate each 320 MHz segment of bandwidth onto a singlelaser and combine two hundred and fifty laser wavelengths together, thuseliminating the need for RF frequency converters. Depending on thenumber of service beams and feeder beams required, one or the otherconfiguration can be selected to provide the lowest mass solution.

The light emitted by each of the sixty three lasers 432, which can bereferred to as an optical carrier signal, is provided (e.g., via arespective optical fiber) to a respective one of the sixty threeseparate EOMs 434_1 to 434_63. The EOMs can be referred to individuallyas an EOM 434, or collectively as the EOMs 434. Each of the EOMs 434 isan optical device in which a signal-controlled element exhibiting anelectro-optic effect is used to modulate a respective beam of light. Themodulation performed by the EOMs 434 may be imposed on the phase,frequency, amplitude, or polarization of a beam of light, or anycombination thereof. In accordance with a specific embodiment, each ofthe EOMs 434 is a phase modulating EOM that is used as an amplitudemodulator by using a Mach-Zehnder interferometer. In other words, eachof the EOMs 434 can be implemented as a Mach-Zehnder modulator (MZM),which can be a Lithium Niobate Mach-Zehnder modulator, but is notlimited thereto. In accordance with specific embodiments, each of theEOMs 434 is implemented as an MZM that produces an amplitude modulated(AM) optical waveform with a modulation index between 10% and 80% inorder to maintain fidelity of an RF waveform (modulated therein) withouttoo much distortion. The optical signal that is output by each of theEOMs 434 can be referred to as an optical data signal. The modulationscheme that is implemented by the EOMs 434 can result in double- orvestigial-sidebands, including both an upper sideband (USB) and a lowersideband (LSB). Alternatively single-sideband modulation (SSB) can beutilized to increase bandwidth and transmission power efficiency.

The sixty three separate optical data signals that are output by thesixty three EOMs 434 are provided to the WDM MUX 436, which can also bereferred to as a dense wavelength division multiplexing (DWDM) MUX. TheWMD MUX 436 multiplexes (i.e., combines) the sixty three optical datasignals, received from the sixty three EOMs 434, onto a single opticalfiber, with each of the sixty three separate optical data signals beingcarried at the same time on its own separate optical wavelength within aspecified contiguous wavelength range (e.g., from 1560 nm to 1575 nm) ornon-contiguous wavelength range (e.g., from 1510 nm to 1534.8 nm, andfrom 1540.2 nm to 1564.8 m). For example, as explained above, the sixtythree optical data signals can have peak wavelengths that occur at 0.2nm intervals from 1560 nm to 1572.8 nm.

The signal that is output by the WMD MUX 436, which can be referred toas a wavelength division multiplexed optical signal, is provided to theoptical amplifier (OA) 438. The OA 438 amplifies the wavelength divisionmultiplexed optical signal so that the wavelength division multiplexedoptical signal has sufficient power to enable transmission thereof fromthe satellite 100 in free-space to the gateway 105. The OA 438 can be anerbium-doped fiber amplifier (EDFA), but is not limited thereto. Theoutput of the OA 438 can be referred to as an optically amplifiedwavelength division multiplexed optical signal.

The optically amplified wavelength division multiplexed optical signal,which is output by the OA 438, is provided (e.g., via an optical fiber)to the transmitter optics 440. The transmitter optics 440, which canalso be referred to as a telescope, can includes optical elements suchas lenses, mirrors, reflectors, filters and/or the like. The transmitteroptics 440 outputs a collimated optical feeder downlink beam that isaimed at a ground based optical gateway (e.g., 105). A gimbal, and/orthe like, can be used to control the steering of the transmitter optics440. In accordance with an embodiment, the collimated optical feederdownlink beam has an aperture of about 40 cm, and a half beam divergenceof about 0.0000012 radians, wherein the term “about” as used hereinmeans +/−10 percent of a specified value. The use of other apertures andhalf beam divergence values are also within the scope of the embodimentsdescribed herein. The collimated optical feeder downlink beam, which isoutput by the transmitter optics 440, is transmitted in free-space toreceiver optics in the gateway 105.

A space segment (e.g., a satellite 100) can have different optics thatare used for transmitting an optical feeder downlink beam (e.g., 102 d)to a gateway, than the optics that are used for receiving an opticalfeeder uplink beam (e.g., 102 u) from a gateway. Alternatively, andpreferably, to reduce the weight that needs to be carried by the spacesegment (e.g., a satellite 100), the same optics can be used for bothtransmitting an optical feeder downlink beam (e.g., 102 d) to a gatewayand for receiving an optical feeder uplink beam (e.g., 102 u) from agateway. More specifically, the TX optics 440 shown in FIG. 4D can bethe same as the RX optics 302 shown in FIG. 3. Additional and/oralternative components can be shared between the space segment forwardlink equipment shown in FIG. 3 and the space segment return linkequipment shown in FIGS. 4A, 4B and 4D. For example, the feed horns 326in FIG. 3 can be the same as the feed horns 402 shown in FIGS. 4A and4B. For another example, the OMJs 324 in FIG. 3 can be the same as theOMJs 404 in FIGS. 4A and 4B, if the OMJs are implement as a three-portdevice. These are just a few example, which are not intended to be allencompassing.

Referring again to the EOMs 434 in FIG. 4D, in accordance with certainembodiments of the present technology, each of the EOMs 434 modulatesthe optical signal it receives (e.g., via an optical fiber from arespective laser 432) with a separate RF signal that has already beenmodulated to include user data. For example, the EOM 434_1 modulates theoptical signal it receives from the laser 431 1 with a data modulated RFcarrier signal it receives from the combiner 420_1 (in FIG. 4A) or fromthe combiner 423_1 (in FIG. 4B). The data modulated RF carrier signalthat the EOM 434_1 receives from a combiner (420_1 in FIG. 4A, or 423_1in FIG. 4B) can include data corresponding to eight service uplink beamsreceived from service terminals STs. Similarly, the EOMs 434_2 to 434_62can each receive a different data modulated RF carrier signal, from adifferent combiner 420 or 423, with each data modulated RF carriersignal corresponding to a different group of eight service uplink beamsreceived from service terminals STs. The EOM 434_63 can receive a datamodulated RF carrier signal, from a combiner 420 or 423, wherein thedata modulated RF carrier signal corresponds to four service uplinkbeams received from service terminals STs. In this manner, the EOMs 434can be collectively provided with data modulated RF carrier signalscorresponding to five hundred service uplink beams (i.e., 62*8+1*4=500).

In the embodiments described above with reference to FIGS. 4A-4D, thecollimated optical feeder downlink beam (that is output by thetransmitter optics 440 and provided to a ground based optical gateway,e.g., 105) was shown and described as including data corresponding to aplurality of (e.g., five hundred) service uplink beams received from aplurality of service terminals STs. In alternative embodiments, thecollimated optical feeder downlink beam (that is output by thetransmitter optics 440 and provided to a ground based optical gateway,e.g., 105) includes data corresponding to a plurality service uplinkbeams received from a plurality service terminals STs, as well as datacorresponding to one or more ISL beams received from one or more othersatellites. For example, as shown in FIG. 4E, in addition to receivingoptical signals output by a plurality (e.g., sixty two) EOMs 434, theWDM MUX 436 is also shown as receiving an amplified optical ISL signalproduced by receiver optics 452 and an optical amplifier (OA) 458. Morespecifically, the receiver optics 452 of space segment return linkequipment 400E is configured to receive an optical ISL beam that istransmitted through free-space by transmitter optics of anothersatellite, and the receiver optics 452 provides an optical ISL signaloutput therefrom (e.g., via an optical fiber) to the OA 458. Thereceiver optics 452, which can also be referred to as a telescope, canincludes optical elements such as mirrors, reflectors, filters and/orthe like, as was the case with the receiver optics 302. A gimbal, and/orthe like, can be used to control the steering of the receiver optics452, as was the case with the receiver optics 302. Both the receiveroptics 302 (used to receive an optical feeder uplink beam) and thereceiver optics 452 (used to receiver an optical ISL beam) can beincluded in the same satellite. It would also be possible to use thesame receiver optics (e.g., 302) to receive an optical feeder uplinkbeams during certain periods of time, and to receive an optical ISL beamduring other periods of time. The same receiver optics (e.g., 302)cannot be used to receive an optical feeder uplink beam and an opticalISL beam at the same time, because the receiver optics would need to beaimed differently to receive the optical ISL beam from another satellitethan it would need to be aimed to receive the optical feeder uplink beamfrom a ground based optical gateway. Accordingly, in order to receive anoptical feeder uplink beam and an optical ISL beam at the same time asatellite should include first receiver optics for use in receiving anoptical feeder uplink beam, and second receiver optics for use inreceiving an optical ISL beam. Third receiver optics can also beincluded on the satellite for use as a backup which can be used tobackup either the first or second receiver optics, if one of those wereto fail. Additional backup receiver optics may also be included on asatellite. Further receiver optics can be added if there was a desire toreceive optical ISL beams from more than one other satellite at the sametime, in which the WDM MUX 436 can receive two or more optical ISLsignals at the same time, and can multiple those ISL signals withoptical signals (including data corresponding to a plurality of serviceuplink beams received from a plurality of service terminals STs) into asingle collimated optical feeder downlink beam (that is output by thetransmitter optics 440 and provided to a ground based optical gateway,e.g., 105). However, it should be noted that it may be beneficial tolimit the amount of receiver optics included on a satellite to limit theweight of the satellite. Optionally, a wavelength converter 454 and/or afrequency converter 456 can be located between the receiver optics 452and the optical amplifier 458, or alternatively between the opticalamplifier 458 and the WDM MUX 436. The function and benefits of awavelength and a frequency converter are described above, and thus, neednot be repeated.

Gateway Return Link Equipment

FIG. 5A will now be used to describe gateway return link equipment 500A,according to an embodiment of the present technology. Such gatewayreturn link equipment 500A can also be referred to as an optical gatewayreturn link subsystem 500A, or more generally, as an opticalcommunication subsystem. Referring to FIG. 5A, the optical gatewayreturn link subsystem 500A is shown as including receiver optics 502, anoptical amplifier (OA) 504, a wavelength-division multiplexing (WDM)demultiplexer (DEMUX) 506, sixty three photodetectors (PDs) 508_1 to508_63, sixty three filters 510_1 to 510_63, sixty three low noiseamplifiers (LNAs) 512_1 to 512_63, and sixty three frequencydown-converters 514_1 to 514_63. The optical gateway return linksubsystem 500A is also shown as including sixty three demodulator anddigital signal processor (DSP) blocks 516_1 to 516_63, and four localoscillators (LOs) 522_1 to 522_4 (which can be referred to individuallyas an LO 522, or collectively as the LOs 522).

The receiver optics 502, which can also be referred to as a telescope,can includes optical elements such as mirrors, reflectors, filtersand/or the like. The receiver optics 502 receives the optical feederdownlink beam (e.g., 102 d) that is transmitted through free-space froma space segment (e.g., a satellite 100), by the space based return linksubsystem 400C (or 400A or 400B) and 400D, and provides the receivedoptical feeder downlink beam (e.g., via an optical fiber) to the OA 504.A gimbal, and/or the like, can be used to control the steering of thereceiver optics 502. When the optical feeder downlink beam reaches thegateway, the power of the optical feeder downlink beam is significantlyattenuated compared to when it was transmitted by the space based returnlink subsystem. Accordingly, the OA 504 is used to amplify the receivedoptical feeder downlink beam before it is provided to the WDM DEMUX 506.The OA 504 can be, e.g., an erbium-doped fiber amplifier (EDFA), but isnot limited thereto. The output of the OA 504 can be referred to as anoptically amplified received optical feeder downlink beam. The WDM DEMUX506 demultiplexes (i.e., separates) the received optical feeder uplinkbeam (after it has been optically amplified) into sixty three separateoptical signals, each of which is provided to a separate photodetector(PD) 508. Each PD 508 converts the optical signal it receives from theWDM DEMUX 506 to a respective RF electrical signal. The RF electricalsignal produced by each PD 508 is provided to a respective filter (FTR)510 (e.g., a bandpass filter) to remove unwanted frequency componentsand/or enhance desired frequency components. For an example, wherefrequency down-conversions were performed on the satellite (by the spacesegment return link equipment 400A or 400B), each filter 510 can passfrequencies within the range of 6.70-7.2 GHz, or within the range of6.3-7.2 GHz, but are not limited thereto. For another example, wherefrequency down-conversions were not performed on the satellite (e.g., bythe space segment return link equipment 400C), each filter 510 can passfrequencies within the range of 29.5-30 GHz, but are not limitedthereto. The filtered RF electrical signal, which is output by eachfilter 408, is provided to a respective low noise amplifier (LNA) 512.Each LNA 512 amplifies the relatively low-power RF signal it receivesfrom a respective filter 510 without significantly degrading the signalssignal-to-noise ratio. The amplified RF signal that is output by eachLNA 512 is provided to a respective frequency down-converter 514, theoutput of which is provided to a respective demodulator and DSP block516.

Each frequency down-converter 514 receives an RF signal from an LNA 512(which RF signal includes data from subscriber terminals STs, and thus,can be referred to as an RF data signal) and an RF signal from an LO 452(which can be referred to as an LO signal), and uses the LO signal todown-convert the RF data signal to baseband. The baseband data signaloutput by each frequency down-converter 514 is provided to a respectivedemodulator and DSP block 516. Each demodulator and DSP block 516demodulates the baseband data signal it receives, and performs digitalsignal processing thereon. Such a demodulated data signal can be used toprovide data to, or request data from, a server, client and/or the likethat is coupled to a network (e.g., the network 140 in FIG. 1).

A gateway (e.g., 105) can have different optics that are used fortransmitting an optical feeder uplink beam (e.g., 102 u) to a spacesegment (e.g., satellite 100), than the optics that are used forreceiving an optical feeder downlink beam (e.g., 102 d) from a spacesegment. Alternatively, a gateway can use the same optics for bothtransmitting an optical feeder uplink beam (e.g., 102 u) to a spacesegment and for receiving an optical feeder downlink beam (e.g., 102 d)from a space segment. More specifically, the RX optics 502 shown in FIG.5A can be the same as the TX optics 210 shown in FIG. 2A.

FIG. 5B depicts gateway return link equipment 500B according to anotherembodiment of the present technology, wherein the gateway return linkequipment 500B provides one or more optical signals to one or moreoptical networks that are external to the optical gateway that includesthe gateway return link equipment 500B. More specifically, FIG. 5B showsthat one or more of the optical signals that are output from WDM DEMUX506 may be provided to optical fiber(s) of or attached to opticalnetwork(s) (such as, but not limited to, LAN, MAN or WAN) external tothe optical gateway in which the gateway return link equipment 500B islocated. This embodiment enables, for example, a payload on a satelliteto communicate end-to-end with an optical network, external to thegateway, without the gateway needing to perform any demodulation ordecryption of signals being provided from the payload on the satelliteto a ground based optical network external to the ground based gateway.Although not specifically shown in FIG. 5B, each optical signal paththat provides an optical signal from the WDM DEMUX 506 to an opticalnetwork external to the optical gateway may include a filter to removeunwanted frequencies and/or an optical amplifier (OA) to amplify theoptical signal before it is provided to the external optical network.Exemplary details of such filters and OAs have been described herein,and thus, need not be repeated. Since each of the optical signals outputfrom the WDM DEMUX 506 will have a different optical wavelength, theoptical signals provided to the external optical networks will have anoptical wavelength that differs from the wavelengths of the othersignals output by the WDM DEMUX 506. Optionally, the wavelength ofoptical signals being provided to an external optical network can beconverted to another optical wavelength, before the optical signal isprovided to the external optical network. One or more optical wavelengthconverters, within or external to the optical gateway, can be used toperform such wavelength conversions. The embodiments described withreference to FIG. 5B (as well as FIG. 2D, discussed above) can provideenhanced end-to-end security, e.g., for military and/or other governmentdata, because the gateway does not need any knowledge of the modulationand/or encryption schemes used on the optical signals that are beingreceived from and/or forwarded to the optical network(s) that is/areexternal to the optical gateway.

In accordance with certain embodiments, the gateway return linkequipment 500B can optionally include wavelength converters 532, whereineach of the wavelength converters 532 is configured to convert a peakoptical wavelength of one of the one or more optical data signals, thatis being provided to one of the one or more optical networks that areexternal to the ground based optical gateway (that includes the gatewayreturn link equipment 500B), to a different peak optical wavelengthbefore the one of the one or more optical data signals is provided tothe one of the one or more optical networks that are external to theground based optical gateway. Additionally, or alternatively, thegateway return link equipment 500B can optionally include one or morefrequency converters 534, wherein each of the frequency converters 534is configured to up-convert or down-convert a frequency of at least oneof the one or more optical data signals, that is being provided to oneof the one or more optical networks that are external to the groundbased optical gateway (that includes the gateway return link equipment500B), before optical data signal(s) is/are provided to the opticalnetwork(s) that are external to the ground based optical gateway.Wavelength conversion can be performed prior to the frequencyconversion, as shown in FIG. 5B, or alternatively, frequency conversioncan be performed prior to the wavelength conversion. For example, therelative positions of the wavelength converters 532 and the frequencyconverters 534 in FIG. 5B can be swapped. Additionally, opticalamplification (using an optical amplifier similar to the opticalamplifier 504) and/or optical filtering can be done downstream of theWDM DE-MUX 506 before one or more of the optical outputs of the WDMDE-MUX 506 is/are provided to the optical network(s) that are externalto the ground based optical gateway.

Methods to Produce and Transmit an Optical Feeder Uplink Beam

FIG. 6 will now be used to summarize methods for enabling a ground basedsubsystem (e.g., the gateway forward link equipment 200 in FIG. 2A) toproduce and transmit an optical feeder uplink beam (e.g., 102 u inFIG. 1) to a satellite (e.g., 100 in FIG. 1) that is configured toreceive the optical feeder uplink beam and in dependence thereon produceand transmit a plurality of RF service downlink beams (e.g., 106 d, 110d, 114 d and 118 d in FIG. 1) within a specified RF frequency range toservice terminals STs. In accordance with certain embodiments, thespecified RF frequency range within which the satellite is configured toproduce and transmit a plurality of RF service downlink beams is adownlink portion of the Ka band. The downlink portion of the Ka band canbe from 17.7 GHz to 20.2 GHz, and thus, have a bandwidth of 2.5 GHz.Alternatively, the downlink portion of the Ka band can be from 17.3 GHzto 20.2 GHz, and thus, have a bandwidth of 2.9 GHz. These are just a fewexamples, which are not intended to be all encompassing.

Referring to FIG. 6, step 602 involves emitting a plurality of opticalsignals (e.g., two hundred and fifty optical signals) each having adifferent peak wavelength that is within a specified optical wavelengthrange. Step 602 can be performed using the lasers 202 discussed abovewith reference to FIG. 2A. The specified optical wavelength range may bewithin the C-band and/or L-band optical wavelengths, as explained above.Further, as explained above, the specified optical wavelength range canbe a contiguous optical wavelength range within an IR spectrum, or anon-contiguous optical wavelength range within the IR spectrum. As notedabove, visible and/or other optical wavelengths may alternatively beused.

Step 604 involves electro-optically modulating each of the opticalsignals with one of a plurality of different data modulated RF carriersignals, each of which has been modulated to carry data for at least oneof the plurality of RF service downlink beams, to thereby produce aplurality of optical data signals, each of which carries data for atleast one of the plurality of RF service downlink beams and has an RFfrequency within the same specified RF frequency range within which thesatellite is configured to transmit the plurality of RF service downlinkbeams. Step 604 can be performed using the EOMs 204 discussed above withreference to FIG. 2A.

Step 606 involves multiplexing the plurality of optical data signals tothereby produce a wavelength division multiplexed optical signal thatincludes data for the plurality of RF service downlink beams. Step 606can be performed using the WDM MUX 206 discussed above with reference toFIG. 2A.

Step 608 involves producing an optical feeder uplink beam, in dependenceon the wavelength division multiplexed optical signal, and step 610involves transmitting the optical feeder uplink beam through free-spaceto the satellite. Steps 608 and 610 can be performed by the transmitteroptics 210 discussed above with reference to FIG. 2A. The opticalamplifier (OA) 208 discussed above with reference to FIG. 2A can also beused to perform step 608.

Beneficially, because the RF frequencies of the optical data signalsproduced during the electro-optically modulating step 604 are within thesame specified RF frequency range within which the satellite isconfigured to transmit the plurality of RF service downlink beams, thereis an elimination of any need for the satellite to perform any frequencyconversions when producing the plurality of RF service downlink beams independence on the optical feeder uplink beam. In other words, the spacesegment forward link equipment 300 in FIG. 3 beneficially does not needany frequency down-converters or any other type of frequency conversionequipment.

A method can also include receiving a plurality of RF carrier signalseach of which has a different RF frequency within the same specified RFfrequency range within which the satellite is configured to transmit theplurality of RF service downlink beams, and producing the modulated RFsignals, which are electro-optically modulated with the optical signals,in dependence on the plurality of RF carrier signals. The RF carriersignals can be produce by one or more local oscillators 222 discussedabove with reference to FIG. 2B. The modulated RF signals can beproduced by RFMs 224 discussed above with reference to FIG. 2B. Furtherdetails of the methods described with reference to FIG. 6 can beappreciated from the above description of FIGS. 1-5.

Methods to Produce and Transmit RF Service Downlink Beams

FIG. 7 will now be used to summarize methods for enabling a space basedsubsystem (e.g., the space segment forward link equipment 300 of FIG. 3)of a satellite (e.g., 100) to produce and transmit a plurality of RFservice downlink beams (e.g., 106 d, 110 d, 114 d and 118 d in FIG. 1)within a specified RF frequency range to service terminals STs. Inaccordance with certain embodiments, the specified RF frequency rangewithin which the satellite is configured to produce and transmit aplurality of RF service downlink beams is a downlink portion of the Kaband. The downlink portion of the Ka band can be from 17.7 GHz to 20.2GHz, and thus, have a bandwidth of 2.5 GHz. Alternatively, the downlinkportion of the Ka band can be from 17.3 GHz to 20.2 GHz, and thus, havea bandwidth of 2.9 GHz. These are just a few examples, which are notintended to be all encompassing.

Referring to FIG. 7, step 702 involves receiving an optical feederuplink beam (e.g., 102 u) from a ground based subsystem (e.g., thegateway forward link equipment 200 in FIG. 2A). Step 702 can beperformed by the receiver optics 302 described above with reference toFIG. 3.

Step 704 involves producing, in dependence on the received opticalfeeder uplink beam, a plurality of (e.g., two hundred and fifty)separate optical signals that each have a different peak wavelength.Step 704 can be performed by the WDM-DEMUX 306 described above withreference to FIG. 3.

Step 706 involves converting each of the separate optical signals into arespective electrical data signal having an RF frequency within the samespecified RF frequency range within which the space based subsystem isconfigured to transmit the plurality of RF service downlink beams. Step706 can be performed by the PDs 308 discussed above with reference toFIG. 3.

Step 708 involves producing, in dependence on the electrical datasignals, the plurality of RF service downlink beams within the specifiedRF frequency range. Step 708 can be performed, e.g., by the filters 310,LNAs 312, splitters 314, HPAs 318, HFs 320, OMJs 324, and feed horns 326discussed above with reference to FIG. 3.

Step 710 involves transmitting the plurality of RF service downlinkbeams within the specified RF frequency range. Step 710 can be performedby the feed horns 326 discussed above with reference to FIG. 3, and moregenerally, antenna systems.

Beneficially, because the RF frequencies of the electrical data signalsresulting from the converting step 706 are within the same specified RFfrequency range within which the space based subsystem is configured totransmit the plurality of RF service downlink beams, there is anelimination of any need for the space based subsystem (e.g., the spacesegment forward link equipment 300 in FIG. 3) to perform any frequencyconversions when producing the plurality of RF service downlink beams independence on the optical feeder uplink beam. In other words,beneficially the space segment forward link equipment 300 in FIG. 3 doesnot need any frequency down-converters or any other type of frequencyconversion equipment. Further details of the methods described withreference to FIG. 7 can be appreciated from the above description ofFIGS. 1-5.

Methods to Produce and Transmit Optical Feeder Downlink Beams

FIG. 8 is a high level flow diagram that is used to summarize methodsfor enabling a space based subsystem of a satellite to produce andtransmit an optical feeder downlink beam (e.g., 102 d) within aspecified optical wavelength range, according to certain embodiments ofthe present technology. More specifically, certain methods describedwith reference to FIG. 8 enable a space based subsystem of a satellite(e.g., 100) to produce and transmit an optical feeder downlink beam independence on RF service uplink beams received from service terminalswithin a specified RF frequency range. The specified optical wavelengthrange may be within the C-band and/or L-band optical wavelengths, butare not limited thereto. Further, as explained above, the specifiedoptical wavelength range can be a contiguous optical wavelength rangewithin an IR spectrum, or a non-contiguous optical wavelength rangewithin the IR spectrum. As noted above, visible and/or other opticalwavelengths may alternatively be used.

Referring to FIG. 8, step 802 involves emitting a plurality of opticalsignals (e.g., sixty three optical signal) each having a different peakwavelength that is within a specified optical wavelength range. Step 802can be performed by the lasers 432 discussed above with reference toFIG. 4D.

Step 804 involves electro-optically modulating each of the opticalsignals with one of a plurality of different data modulated RF carriersignals, each of which has been modulated to carry return link data forat least one of a plurality of RF service uplink beams, to therebyproduce a plurality of optical data signals, each of which carriesreturn link data for at least one of the plurality of RF service uplinkbeams and has an RF frequency within the same specified RF frequencyrange within which the satellite is configured to receive RF serviceuplink beams from service terminals. Step 804 can be performed by theEOMs 434 discussed above with reference to FIG. 4D.

Step 806 involves multiplexing the plurality of optical data signals tothereby produce a wavelength division multiplexed optical signal thatincludes return link data corresponding to the RF service uplink beams.Step 806 can be performed by the WDM multiplexer 436 discussed abovewith reference to FIG. 4D.

Step 808 involves producing an optical feeder downlink beam, independence on the wavelength division multiplexed optical signal, andstep 810 involves transmitting the optical feeder downlink beam throughfree-space from the satellite to a ground based gateway. Steps 808 and810 can be performed by the transmitter optics 440 discussed above withreference to FIG. 4D.

In accordance with certain embodiments, where RF frequencies of theoptical data signals produced during the electro-optically modulatingare within the same specified RF frequency range within which thesatellite is configured to receive RF service uplink beams from serviceterminals, there is an elimination of any need for the satellite toperform any frequency conversions when producing the optical feederdownlink beam in dependence on the RF service uplink beams. In otherwords, in such embodiments, the space segment return link equipmentbeneficially does not need any frequency down-converters or any othertype of frequency conversion equipment. The space segment return linkequipment 400C (in FIG. 4C) and 400D (in FIG. 4D), for example, can beused to producing an optical feeder downlink beam without the need forthe satellite to perform any frequency conversions. In accordance withcertain embodiments, the specified RF frequency range within which thesatellite is configured to receive RF service uplink beams from serviceterminals is an uplink portion of the Ka band. The uplink portion of theKa band can be from 29.5-30 GHz, and thus, have a bandwidth of 0.5 GHz.This is just an example, which are not intended to be all encompassing.

A method can also include receiving a plurality of RF service uplinkbeams, and producing the plurality of data modulated RF carrier signalsthat have been modulated to carry the return link data corresponding tothe RF service uplink beams received from the service terminals. Furtherdetails of the methods described with reference to FIG. 8 can beappreciated from the above description of FIGS. 1-5.

Space Segment Forward Inter-Satellite Link Equipment

FIG. 9A will now be used to describe a portion of space segment forwardinter-satellite link (ISL) equipment 900A, according to an embodiment ofthe present technology. Such space segment forward ISL equipment 900A,which can also be referred to as a satellite forward ISL subsystem 900A,or more generally, as an optical communication subsystem, can beconfigured to receive an optical feeder uplink beam that is transmittedfrom the ground based optical gateway subsystem 200A or 200D (in FIG. 2Aor 2D) to the satellite (e.g., 100) that is carrying the space segmentforward ISL equipment 900. Alternatively, or additionally, the spacesegment forward ISL equipment 900A can be configured to receive anoptical ISL beam that is transmitted from another satellite (e.g., 150).The space segment forward ISL equipment 900A can also configured to actas an optical repeater to pass on an optical beam (or a portion thereof)that it receives (from the ground based optical gateway subsystem 200Aor 200D, or from another satellite) to a further satellite (e.g., 160)as an optical ISL beam. Both the space segment forward link equipment300, described above with reference to FIG. 3, and the space segmentforward ISL equipment 900A, which will be described below with referenceto FIG. 9A, can be included on a same satellite (e.g., 100). This canenable the satellite (e.g., 100) to send some data that it receives(e.g., from the gateway 105) to some service terminals STs that arewithin a region (e.g., 108) that is illuminated by a service downlinkbeam (e.g., 106 d) of the satellite, and send other data that itreceives (from the same gateway 105) to another satellite (e.g., 150) sothat the other satellite can send the other data to other serviceterminal STs that are within another region that is illuminated by aservice downlink beam of the other satellite. In such an embodiment, thespace segment forward ISL equipment 900A can share certain elements withthe space segment forward link equipment 300, as will be appreciatedfrom the description of FIG. 9A. The elements that are shared arelabeled the same as they were in FIG. 3.

Referring to FIG. 9A, the space segment forward ISL equipment 900A isshown as including receiver optics 302, an optical amplifier (OA) 304, awavelength-division multiplexing (WDM) demultiplexer (DEMUX) 306, twohundred and fifty beam splitters (BS) 932_1 to 932_250, awavelength-division multiplexing (WDM) multiplexer (MUX) 936, an opticalamplifier (OA) 938 and transmitter optics 940.

The receiver optics 302 (which can include optical elements such asmirrors, reflectors, filters and/or the like) can receive an opticalfeeder uplink beam (e.g., 102 u) that is transmitted through free-spaceto the satellite by the ground based optical gateway forward linksubsystem 200A or 200D, and provides the received optical feeder uplinkbeam (e.g., via an optical fiber) to the OA 304. A gimbal, and/or thelike, can be used to control the steering of the receiver optics 302.When the optical feeder uplink beam reaches the satellite, the power ofthe optical feeder uplink beam is significantly attenuated compared towhen it was transmitted by the ground based optical gateway subsystem(e.g., 200A or 200D). Accordingly, the OA 304 is used to amplify thereceived optical feeder uplink beam before it is provided to the WDMDEMUX 306. The OA 304 can be, e.g., an erbium-doped fiber amplifier(EDFA), but is not limited thereto. The output of the OA 304 can bereferred to as an optically amplified received optical feeder uplinksignal.

The same receiver optics 302, or another instance of the receiveroptics, can receive an optical ISL beam that is transmitted by anothersatellite (e.g., 150) through free-space to the satellite (e.g., 100),and provides the received optical ISL beam (e.g., via an optical fiber)to the OA 304, or another instance of the OA. When an optical ISL beamthat originated from another satellite reaches the satellite, the powerof the optical ISL beam is significantly attenuated compared to when itwas transmitted by the other satellite. Accordingly, the OA 304 can beused to amplify the received optical ISL beam before it is provided tothe WDM DEMUX 306. In this case, the output of the OA 304 can bereferred to as an optically amplified received optical ISL signal.

The WDM DEMUX 306 demultiplexes (i.e., separates) the received opticalfeeder uplink beam (or the received optical ISL beam), after it has beenoptically amplified, into two hundred and fifty separate optical datasignals, each of which has a different peak optical wavelength, and eachof which is provided to a separate beam splitter (BS) 932. Each BS 932splits the optical data signal it receives into two optical datasignals, which include the same data, but may have different power,depending upon how the BS is implemented. Unless stated otherwise, itwill be assumed that each BS 932 splits the optical data signal itreceives from the WDM MUX 306 into two optical data signals having thesame content and power (i.e., two substantially identical optical datasignals). The two optical data signals that are output by each BS 932can be provided to an optional pair of optical filters (FTR) 934. Forexample, one of the optical signals output by the BS 932_1 can beprovided to a filter 934_1 a, and the other optical signal output by theBS 932_1 can be provided to the filter 934_1 b. The two filters thatfilter the two optical data signals output by the same BS 932 can filterthe two optical data signals in the same manner, or in differentmanners, depending upon implementation. It is also possible that one orboth of the optical data signals that are output by a BS 932 is/are notfiltered before being passed onto the next element in its optical signalpath. For example, it is possible that one of the optical data signalsoutput by the BS 932_1 is provided directly to the WDM MUX 936, and/orthat the other one of the optical data signals output by the BS 932_1 isprovided directly to the PD 308_1. It is also possible that additionalelements not specifically shown can be included in the optical signalpaths.

The two hundred and fifty optical data signals that are provided by thetwo hundred and fifty beam splitters 932_1 to 932_250 to the WDM MUX 936(which signals, as noted above, may or may not first be filtered by arespective one of the filters 934) are multiplexed (i.e., combined) bythe WDM MUX 936 onto a single optical fiber, with each of the twohundred and fifty optical data signals being carried at the same time onits own separate optical wavelength within a specified contiguouswavelength range (e.g., from 1510 nm to 1560 nm) or a specifiednon-contiguous wavelength range (e.g., from 1510 nm to 1534.8 nm andfrom 1540.2 nm to 1564.8 nm). However, wider or narrow wavelengthranges, within the infrared or other parts of the optical spectrum, mayalternatively be used. For example, it would also be possible to utilizea contiguous or non-contiguous wavelength range within the 400 nm-700 nmvisible spectrum.

The OA 938 amplifies the wavelength division multiplexed optical signalso that the wavelength division multiplexed optical signal hassufficient power to enable transmission thereof from the satellite(e.g., 100) in free-space to another satellite (e.g., 150). The OA 938can be an erbium-doped fiber amplifier (EDFA), but is not limitedthereto. The output of the OA 938 can be referred to as an opticallyamplified wavelength division multiplexed optical ISL signal.

The optically amplified wavelength division multiplexed optical ISLsignal, which is output by the OA 938, is provided (e.g., via an opticalfiber) to the transmitter optics 940. The transmitter optics 940, whichcan also be referred to as a telescope, can includes optical elementssuch as lenses, mirrors, reflectors, filters and/or the like. Thetransmitter optics 940 outputs a collimated optical ISL beam that isaimed at another satellite. A gimbal, and/or the like, can be used tocontrol the steering of the transmitter optics 940. In accordance withan embodiment, the collimated optical ISL beam has an aperture of about40 cm, and a half beam divergence of about 0.0000012 radians, whereinthe term “about” as used herein means +/−10 percent of a specifiedvalue. The use of other apertures and half beam divergence values arealso within the scope of the embodiments described herein. Thecollimated optical ISL beam, which is output by the transmitter optics940, is transmitted in free-space to receiver optics of anothersatellite.

Still referring to FIG. 9A, the two hundred and fifty beam splitters932_1 to 932_250 also provide two hundred and fifty optical data signalsto two hundred and fifty photodetectors (PDs) 308_1 to 308_250, whichare part of the space segment forward link equipment 300. These twohundred and fifty optical data signals may be filtered by the optionaloptical filters 934_1 b to 934_250 b before being provided to the PDs308_1 to 308_250. In a similar manner, as was discussed above withreference to FIG. 3, each PD 308 converts the optical signal it receivesto a respective RF electrical signal. The RF electrical signal producedby each PD 308 is provided to a respective filter (FTR) 310 (e.g., abandpass filter) to remove unwanted frequency components and/or enhancedesired frequency components. For an example, each filter 310 can passfrequencies within the range of 17.7-20.2 GHz, or within the range of17.3-20.2 GHz, but are not limited thereto. The filtered RF electricalsignal, which is output by each filter 310, is provided to a respectivelow noise amplifier (LNA) 312. Each LNA 312 amplifies the relativelylow-power RF signal it receives from a respective filter 310 withoutsignificantly degrading the signals signal-to-noise ratio. The amplifiedRF signal that is output by each LNA 312 is provided to a respectivesplitter 314.

Each splitter 314 splits the amplified RF signal it receives into twocopies, each of which has half the power of the amplified RF signal thatis provided to the input of the splitter 314. Each splitter 314 can beimplemented by a hybrid, but is not limited thereto. In accordance withcertain embodiments of the present technology, one of the RF signalsthat is output by a splitter 314 is used to produce one service beam,and the other RF signal that is output by the same splitter 314 is usedto produce another service beam. Each of the copies of the RF signalthat is output by the splitter 314 is provided to a respective filter316. For example, the splitter 314_1 provides one copy of the RF signalit receives to the filter 316_1, and provides another copy of the RFsignal it receives to the filter 316_2. In accordance with certainembodiments, the pair of filters 316 that receive RF signals from thesame splitter 314 have pass bands that differ from one another. Forexample, the filter 316 1 may have a passband of 17.7-18.95 GHz and thefilter 316 2 may have a passband of 18.95-20.2 GHz. For another example,the filter 316_1 may have a passband of 17.3-18.75 GHz and the filter316_2 may have a passband of 18.75-20.2 GHz. This enables each splitter314 and pair of filters 316, which are fed by the splitter 314, toseparate a signal received by the splitter into two separate RF signalscorresponding to two separate user beams. The use of other passbands arepossible and within the scope of embodiments of the present technology.

Each HPA 318 amplifies the RF signal it receives so that the RF signalhas sufficient power to enable transmission thereof from the satellite100 in space to a service terminal ST, which may be on the ground. EachHPA 318 can be, e.g., a liner traveling wave tube high power amplifier,but is not limited thereto. The signal that is output by each of theHPAs 318 can be referred to as an amplified RF signal. Each HF 320 isused to reduce and preferably remove any distortion in the amplified RFsignal that was caused by a respective HPA 318. Each HF 320 can be,e.g., a waveguide cavity filter, but is not limited thereto. Each TC 322can be used for power monitoring, payload testing and/or performingcalibrations based on signals passing therethrough. Each OMJ 324 addseither right hand circular polarization (RHCP) or left hand circularpolarization (LHCP) to the RF signal that is passed through the OMJ.This allows for color reuse frequency band allocation, wherein eachcolor represents a unique combination of a frequency band and an antennapolarization. This way a pair of feeder beams that illuminate adjacentregions can utilize a same RF frequency band, so long as they haveorthogonal polarizations. Each feed horn 326 converts the RF signal itreceives, from a respective OMJ 324, to radio waves and feeds them tothe rest of the antenna system (not shown) to focus the signal into aservice downlink beam. A feed horn 326 and the rest of an antenna can becollectively referred to as the antenna. In other words, an antenna, asthe term is used herein, can include a feed horn. All or some of thefeed horns 326 can share a common reflector. Such reflector(s) is/arenot shown in the Figures, to simply the Figures.

FIG. 9B shows a portion of space segment forward inter-satellite link(ISL) equipment 900B, according to an alternative embodiment of thepresent technology. Such space segment forward ISL equipment 900B, whichcan also be referred to as a satellite forward ISL subsystem 900B, ormore generally, as an optical communication subsystem, can be configuredto receive an optical feeder uplink beam that is transmitted from theground based optical gateway subsystem 200A or 200D (in FIG. 2A or 2D)to the satellite (e.g., 100) that is carrying the space segment forwardISL equipment 900. Alternatively, or additionally, the space segmentforward ISL equipment 900B can be configured to receive an optical ISLbeam that is transmitted from another satellite (e.g., 150). The spacesegment forward ISL equipment 900B can also configured to act as anoptical repeater to pass on an optical beam (or a portion thereof) thatit receives (from the ground based optical gateway subsystem 200A or200D, or from another satellite) to a further satellite (e.g., 160) asan optical ISL beam. Both the space segment forward link equipment 300,described above with reference to FIG. 3, and the space segment forwardISL equipment 900B, which will be described below with reference to FIG.9B, can be included on a same satellite (e.g., 100). This can enable thesatellite (e.g., 100) to send some data that it receives (e.g., from thegateway 105) to some service terminals STs that are within a region(e.g., 108) that is illuminated by a service downlink beam (e.g., 106 d)of the satellite, and send other data that it receives (from the samegateway 105) to another satellite (e.g., 150) so that the othersatellite can send the other data to other service terminal STs that arewithin another region that is illuminated by a service downlink beam ofthe other satellite. In such an embodiment, the space segment forwardISL equipment 900B can share certain elements with the space segmentforward link equipment 300, as will be appreciated from the descriptionof FIG. 9B. The elements that are shared are labeled the same as theywere in FIG. 3. The elements that are the same in FIG. 9B as they are inFIG. 9A are labeled the same, and need not be described again.

In the embodiment of FIG. 9A, beam slitters 932 were used to split thetwo hundred and fifty separate optical data signals that are output bythe WDM demultiplexer 306 (with each of the optical data signals havinga different peak optical wavelength) into two optical data signals,which include the same data (and share the same peak opticalwavelength). This way, the same data can be included in RF downlinkservice beams (produced by the space segment forward link equipment 300of the satellite) as well as be included in an optical ISL beam(produced by optical-to-optical space segment ISL equipment 900A) andtransmitted to another satellite (which may use the optical ISL beam toproduce its own RF downlink service beams). In the embodiment of FIG.9B, the beam slitters 932 are not included. Rather, a first subset ofthe two hundred and fifty separate optical data signals that are outputby the WDM demultiplexer 306 are used to produce an optical ISL beamthat is transmitted to another satellite (which may use the optical ISLbeam to produce its own RF downlink service beams), and a second subsetof the two hundred and fifty separate optical data signals that areoutput by the WDM demultiplexer 306 are used by the satellite to produceits own RF downlink service beams. In FIG. 9B, the first subset includesone hundred and twenty five optical data signals that are output by theWDM demultiplexer 306, and the second subset includes the other onehundred and twenty five optical data signals that are output by the WDMdemultiplexer 306. It is also possible that the two hundred and fiftyseparate optical data signals that are output by the WDM demultiplexer306 are not equally divided among the first and second subsets. In otherwords, one of the first and second subsets can include a greater numberof optical data signals than the other. It is also possible that the WDMMUX 936 can be eliminated (or at least removed from the optical path) ifonly one of the optical data signals that are output by the WDMdemultiplexer 306 is to be included in an optical ISL beam that is to betransmitted to another satellite. In other words, it is possible that anoptical signal that is output by the WDM demultiplexer 306 is filteredand amplified (but not multiplexed) before it is provided to thetransmitter optics 940 and thereby included in an optical ISL that istransmitted to another satellite.

In the embodiments of FIGS. 9A and 9B, each optical ISL beams is ananalog-over free-space optical signal, which leads to an elegantarchitecture for a satellite repeater, whereby all frequencydown-conversion in the forward link is eliminated. An advantage of thisapproach, especially for HTS satellites, is that it eliminates the needfor very high speed Analog-to-Digital Converters (ADCs) and Digital toAnalog Converters (DACs) on the satellites. Further, this approachallows the aggregation of multiple user links but does not require extrahardware associated with an onboard demodulator and remodulator, andthus reduces the mass, power and cost of the satellite, perhaps makingthe difference between being able to launch or not being able to launchthe satellite.

More generally, in accordance with specific embodiments, the uplink andISL communication signals are modulated at transmit (forward) RFfrequencies that are eventually used to transmit service downlink beamsto service terminals STs, and thus, no frequency conversion in theforward link is required on the satellite, thereby further simplifyingthe payload design. By contrast, previously envisioned free-spaceoptical spacecraft architectures proposed demodulation of the opticalsignal, followed by routing to user link pathways and remodulation ofthe signal on user link (also known as service link) RF frequencies.FIG. 9C shows that one or more of the optical signals that is/are outputby the WDM DEMUX 306 on a satellite can be provided to and consumed byequipment that is located on the satellite, which equipment isgenerically represented by block 950. Examples of such equipment includea command and data handling (C&DH) system, an RF communication payload,and one or more digital payloads. If the equipment 950 is designed toaccept optical signals, one or more optical signals output by the WDMDEMUX 306 can be provided directly to the equipment 950. Alternatively,optical signals can be converted to electrical signals using PDs 308.The optical signals can be filtered prior to being provided to the PDs308, and the electrical signals can be filtered and/or amplifieddownstream of the PDs 308, as shown in FIG. 9C. Exemplary types ofdigital payloads include imaging and/or weather payloads, but are notlimited thereto. A command and data handling system, which can also bereferred to as command and data handling equipment, can be used to carryout commands that are sent from a ground based gateway to the satellite.Such commands can be used to control the propulsion system of thesatellite, steer antennas on the satellite, steer transmitter and/orreceiver optics on the satellite, but are not limited thereto. Where thesatellite includes an imaging payload, commands that are sent from aground based gateway to the satellite can instruct imaging equipment toobtain images, steer imaging equipment, downlink image data, and/or thelike.

In the embodiment shown in FIG. 9C, the optical signals output by theWDM DEMUX 306 are shows as being provided to specific predeterminedsignal paths. For example, certain optical signals are shown as beingprovided to the WDM MUX 936 and being included in an optical ISL beam,other optical signals are shown as being converted to electrical signalsthat are used to produce service downlink beams that are transmitted toservice terminals STs, and still other optical signals are shown asbeing converted to electrical signals that are provided to block 950,which can include, e.g., a command and data handling system, an RFcommunication payload, and/or one or more digital payloads. Inalternative embodiments, such as the one shown in FIG. 9D, flexibilityis increased by including an optical cross-connect switch 960 downstreamof the WDM DEMUX 306. The optical cross-connect switch 960 can be usedto selectively switch the optical signals output by the WDM DEMUX 306among the various signal paths, as desired, e.g., in accordance withcommands provided by the ground based gateway. In FIG. 9D the opticalcross-connect switch 960 is shown as being downstream from some of thefilters 934, but can alternatively be located upstream of some of thefilters, e.g., between the WDM DEMUX 306 and the filters 934.Alternatively, or additionally, a digital cross-connect switch can belocated downstream of the PDs 308 and used to selectively switchelectrical signals (produced by the PDs 308 based on the optical signalsoutput by the WDM DEMUX 306) amount the various signal paths, asdesired, e.g., in accordance with commands provided by the ground basedgateway. In accordance with an embodiment, all of the optical signalsoutput by the WDM DEMUX 306 (before or after being filtered by arespective filter 934) are provided to the optical cross-connect switch960. Alternatively, less than all (e.g., only a subset of) the opticalsignals output by the WDM DEMUX 306 (before or after being filtered by arespective filter 934) are provided to the optical cross-connect switch960. Other variations are possible and within the scope of theembodiments described herein. Various modifications can be made thesubsystem described herein while still being within the scope ofembodiments of the present technology. For example, some or all of thesplitters 314 shown in FIGS. 9A, 9B, 9C and 9D can be eliminated.Additionally, or alternatively, in FIG. 9A some or all of the beamsplitters 932 can be eliminated. Such modifications may simplify thesubsystems, but can reduce the capacity and/or flexibility of thesubsystems. Other modifications can increase the complexity of thesubsystem and increase the capacity and/or flexibility of thesubsystems, e.g., by adding further switches.

Methods for Producing ISL Beams and RF Service Downlink Beams Based onan Optical Feeder Uplink Beam

FIG. 10A is a high level flow diagram that is used to summarize methodsfor enabling a space based subsystem of a satellite (e.g., 100) toproduce to an optical inter-satellite link (ISL) beam (e.g., 152) and RFservice downlink beams (e.g., 106 d, 110 d, 114 d), based on an opticalfeeder uplink beam (e.g., 102 u) received from an optical gateway (e.g.,105), according to an embodiment of the present technology. The steps ofFIG. 10A can be performed, e.g., using the components shown in FIG. 9Adiscussed above.

Referring to FIG. 10A, step 1002 involves receiving an optical feederuplink beam (e.g., 102 u) from a ground based subsystem (e.g., thegateway forward link equipment 200A or 200D in FIG. 2A or 2D). Step 1002can be performed by the receiver optics 302 described above withreference to FIG. 9A.

Step 1004 involves producing, in dependence on the received opticalfeeder uplink beam, N separate optical signals that each have adifferent peak wavelength, where N is an integer that is greater thanone (e.g., N=250). Step 1004 can be performed by the WDM demultiplexer306 described above with reference to FIG. 9A.

Step 1006 involves splitting each of the N separate optical signals(e.g., 250 optical signals) into a respective pair of optical signals,and thereby producing N separate pairs (e.g., 250 separate pairs) ofoptical signals that each have a different peak wavelength within thespecified optical wavelength range, with the optical signals of a samepair having the same peak wavelength. Step 1006 can be performed by thebeam splitters (BSs) 932 described above with reference to FIG. 9A.

Step 1008 involves multiplexing N optical signals that each have adifferent peak wavelength within the specified optical wavelength range,wherein the N optical signals being multiplexed include one of theoptical signals of each of the N separate pairs (e.g., 250 separatepairs) of optical signals, to thereby produce a wavelength divisionmultiplexed optical signal that includes data that is to be forwarded toanother satellite so that the other satellite can transmit, independence thereon, a plurality of RF service downlink beams. Step 1008can be performed by the WDM multiplexer 936 described above withreference to FIG. 9A. As can be appreciated from FIG. 9A, the N opticalsignals may be filtered (e.g., using the filters 934_1 a to 934_250 a)before they are multiplexed at step 1008.

Step 1010 involves producing an optical inter-satellite link (ISL) beamin dependence on the wavelength division multiplexed optical signal, andstep 1012 involves transmitting the optical ISL beam through free-spaceto the other satellite. Steps 1010 and 1012 can be performed by thetransmitter optics 940 described above with reference to FIG. 9A. As canbe appreciated from FIG. 9A, the wavelength division multiplexed opticalsignal may be amplified (e.g., by the optical amplifier 938) before thetransmitter optics 940 are used to perform steps 1010 and 1012. Inaccordance with certain embodiments, RF frequencies of the wavelengthdivision multiplexed optical signal are within the same specified RFfrequency range within which the other satellite (e.g., 150) isconfigured to transmit the plurality of RF service downlink beams,thereby eliminating of any need for the other satellite (e.g., 150) toperform any frequency conversions when producing a plurality of RFservice downlink beams in dependence on the optical ISL beam. Inaccordance with certain embodiments, the specified RF frequency rangewithin which the other satellite (e.g., 150) is configured to produceand transmit a plurality of RF service downlink beams is a downlinkportion of the Ka band. The downlink portion of the Ka band can be from17.7 GHz to 20.2 GHz, and thus, have a bandwidth of 2.5 GHz.Alternatively, the downlink portion of the Ka band can be from 17.3 GHzto 20.2 GHz, and thus, have a bandwidth of 2.9 GHz. These are just a fewexamples, which are not intended to be all encompassing.

Still referring to FIG. 10A, step 1009 involves converting each of Noptical signals, that each have a different peak wavelength within thespecified optical wavelength range, into a respective electrical datasignal having an RF frequency within the same specified RF frequencyrange within which the space based subsystem is configured to transmit aplurality of RF service downlink beams. These N optical signals beingconverted include the other one of the optical signals of each of the Nseparate pairs of optical signals produced by the splitting at step1006. Step 1009, which is similar to step 706 discussed above withreference to FIG. 7, can be performed by the PDs 308 discussed abovewith reference to FIG. 9A.

Step 1011 involves producing, in dependence on the electrical datasignals, the plurality of RF service downlink beams within the specifiedRF frequency range. Step 1011, which is similar to step 708 discussedabove with reference to FIG. 7, can be performed, e.g., by the filters310, LNAs 312, splitters 314, HPAs 318, HFs 320, OMJs 324, and feedhorns 326 discussed above with reference to FIG. 9A.

Step 1013 involves transmitting the plurality of RF service downlinkbeams within the specified RF frequency range. Step 1013, which issimilar to step 710 discussed above with reference to FIG. 7, can beperformed by the feed horns 326 and reflector(s) discussed above withreference to FIG. 9A, and more generally, antenna systems. In accordancewith certain embodiments, because the RF frequencies of the electricaldata signals resulting from the converting (at step 1009) are within thesame specified RF frequency range within which the space based subsystemis configured to transmit the plurality of RF service downlink beams (atstep 1013), there is an elimination of any need for any space basedsubsystem (e.g., 300 and 900A) to perform any frequency conversions whenproducing the plurality of RF service downlink beams in dependence onthe optical feeder uplink beam. In accordance with certain embodiments,the specified RF frequency range within which the satellite (e.g., 100)is configured to produce and transmit a plurality of RF service downlinkbeams is a downlink portion of the Ka band. The downlink portion of theKa band can be from 17.7 GHz to 20.2 GHz, and thus, have a bandwidth of2.5 GHz. Alternatively, the downlink portion of the Ka band can be from17.3 GHz to 20.2 GHz, and thus, have a bandwidth of 2.9 GHz. These arejust a few examples, which are not intended to be all encompassing.

In certain embodiments, step 1006 can be eliminated, in which case steps1009, 1011 and 1013 can also be eliminated. In other words, as notedabove, some or all of the beam splitters 932 shown in FIG. 9A can beeliminated. In other embodiments, step 1006 can involve only splitting asubset of the optical signals produced at step 1004. In other words, ifonly some of the beam splitters 932 are eliminated, then step 1006 caninvolve splitting only a subset of the N separate optical signals into arespective pair of optical signals, and the downstream steps shown inFIG. 10A would be adjusted accordingly. Further, as explained above withreference to FIGS. 9C and 9D, one or more of the optical signals thatresult from step 1004 can be converted to electrical signals using oneor more photodetectors and such electrical signal(s) can be provided toand consumed by equipment that is located on the satellite, such as acommand and data handling (C&DH) system, an RF communication payload,and one or more digital payloads, but not limited thereto. Also, asexplained above with reference to FIG. 9D, switching of optical signalscan be performed, e.g., using the optical cross-connect switch, tocontrol which signals are included in an optical ISL beam, which signalsare converted to RF service downlink beams, and/or which signals areconverted to electrical signals that are provided to and consumed by(e.g., used to control or otherwise used by) equipment located on thesatellite. FIG. 10B is a high level flow diagram that is used tosummarize methods for enabling a space based subsystem of a satellite(e.g., 100) to produce to an optical inter-satellite link (ISL) beam(e.g., 152) and RF service downlink beams (e.g., 106 d, 110 d, 114 d),based on an optical feeder uplink beam (e.g., 102 u) received from anoptical gateway (e.g., 105), according to another embodiment of thepresent technology. The steps of FIG. 10B can be performed, e.g., usingthe components shown in FIG. 9B discussed above.

Steps 1002 and 1004 in FIG. 10B are the same as steps 1002 and 1004 inFIG. 10A, and thus, details of these steps need not be repeated. Adifference between the methods described with reference to FIG. 10A andthe methods described with reference to FIG. 10B is the splitting of theN optical signals that took place in step 1006 of FIG. 10A do not takeplace in FIG. 10B. Rather, in the embodiment of FIG. 10B, a first subsetof the N optical signals (produced at step 1004) are multiplexed at step1008′, and a second subset of the N optical signals (produced at step1004) are converted to electrical data signals at step 1009′.

More specifically, step 1008′ involves multiplexing a first subset ofthe N optical signals that each have a different peak wavelength withina specified optical wavelength range to thereby produce a wavelengthdivision multiplexed optical signal that includes data that is to beforwarded to another satellite so that the other satellite can transmit,in dependence thereon, a plurality of RF service downlink beams. Step1008′ can be performed by the WDM multiplexer 936 described above withreference to FIG. 9B. As can be appreciated from FIG. 9B, the firstsubset of N optical signals may be filtered (e.g., using the filters934_1 to 934_125) before they are multiplexed at step 1008′.

Steps 1010′ and 1012′ in FIG. 10B are similar to steps 1010 and 1012described above with reference to FIG. 10A, except that the optical ISLbeam produced at step 1010′ (and transmitted at step 1012′) is onlyproduced based on the first subset of the N optical signals that aremultiplexed at step 1008′. Steps 1011′ and 1013′ in FIG. 10B are similarto steps 1010 and 1012 described above with reference to FIG. 10A, andthus details thereof need not be described again. Additional details ofsteps 1010′, 1012′, 1011′ and 1013′ can be appreciated from the abovediscussion of FIG. 10A. More generally, additional details of themethods of FIGS. 10A and 10B can be appreciated from the abovediscussion of the space segment equipment described with reference toFIGS. 9A and 9B, as well as other Figures described above.

Further, as explained above with reference to FIGS. 9C and 9D, a thirdsubset of the optical signals that result from step 1004 can beconverted to electrical signals using one or more photodetectors andsuch electrical signal(s) can be provided to and consumed by equipmentthat is located on the satellite, such as a command and data handling(C&DH) system, an RF communication payload, and one or more digitalpayloads, but not limited thereto. Also, as explained above withreference to FIG. 9D, switching of optical signals can be performed,e.g., using the optical cross-connect switch, to control which signalsare included in an optical ISL beam, which signals are converted to RFservice downlink beams, and/or which signals are converted to electricalsignals that are provided to and consumed by (e.g., used to control orotherwise used by) equipment located on the satellite. In other words,which optical signals make up the first subset, the second subset andthe third subset can be changed over time using optical switching.

Methods for Producing ISL Beams and RF Service Downlink Beams Based onan Optical Feeder Uplink Beam

FIG. 11A is a high level flow diagram that is used to summarize methodsfor enabling a space based subsystem of a satellite (e.g., 100) toproduce to an optical inter-satellite link (ISL) beam (e.g., 162) and RFservice downlink beams (e.g., 106 d, 110 d, 114 d), based on an opticalISL beam (e.g., 152) received from another satellite (e.g., 150),according to an embodiment of the present technology. The steps of FIG.11A can be performed, e.g., using the components shown in FIG. 9Adiscussed above.

Referring to FIG. 11A, step 1102 involves receiving an optical ISL beam(e.g., 152) from another satellite (e.g., 150). Step 1102 can beperformed by the receiver optics 302 described above with reference toFIG. 9A.

Step 1104 involves producing, in dependence on the received optical ISLbeam, N separate optical signals that each have a different peakwavelength, where N is an integer that is greater than one (e.g.,N=250). Step 1104 can be performed by the WDM demultiplexer 306described above with reference to FIG. 9A.

Step 1106 involves splitting each of the N separate optical signals(e.g., 250 optical signals) into a respective pair of optical signals,and thereby producing N separate pairs (e.g., 250 separate pairs) ofoptical signals that each have a different peak wavelength within thespecified optical wavelength range, with the optical signals of a samepair having the same peak wavelength. Step 1106 can be performed by thebeam splitters (BSs) 932 described above with reference to FIG. 9A.

Step 1108 involves multiplexing N optical signals that each have adifferent peak wavelength within the specified optical wavelength range,wherein the N optical signals being multiplexed include one of theoptical signals of each of the N separate pairs (e.g., 250 separatepairs) of optical signals, to thereby produce a wavelength divisionmultiplexed optical signal that includes data that is to be forwarded toanother satellite so that the other satellite can transmit, independence thereon, a plurality of RF service downlink beams. Step 1108can be performed by the WDM multiplexer 936 described above withreference to FIG. 9A. As can be appreciated from FIG. 9A, the N opticalsignals may be filtered (e.g., using the filters 934_1 a to 934_250 a)before they are multiplexed at step 1108.

Step 1110 involves producing an optical inter-satellite link (ISL) beamin dependence on the wavelength division multiplexed optical signal, andstep 1112 involves transmitting the optical ISL beam through free-spaceto a further satellite (e.g., 160). Steps 1110 and 1112 can be performedby the transmitter optics 940 described above with reference to FIG. 9A.As can be appreciated from FIG. 9A, the wavelength division multiplexedoptical signal may be amplified (e.g., by the optical amplifier 938)before the transmitter optics 940 are used to perform steps 1110 and1112. In accordance with certain embodiments, RF frequencies of thewavelength division multiplexed optical signal are within the samespecified RF frequency range within which the further satellite (e.g.,160) is configured to transmit the plurality of RF service downlinkbeams, thereby eliminating of any need for the further satellite (e.g.,160) to perform any frequency conversions when producing a plurality ofRF service downlink beams in dependence on the optical ISL beam. Inaccordance with certain embodiments, the specified RF frequency rangewithin which the further satellite (e.g., 160) is configured to produceand transmit a plurality of RF service downlink beams is a downlinkportion of the Ka band. The downlink portion of the Ka band can be from17.7 GHz to 20.2 GHz, and thus, have a bandwidth of 2.5 GHz.Alternatively, the downlink portion of the Ka band can be from 17.3 GHzto 20.2 GHz, and thus, have a bandwidth of 2.9 GHz. These are just a fewexamples, which are not intended to be all encompassing.

Still referring to FIG. 11A, step 1109 involves converting each of Noptical signals, that each have a different peak wavelength within thespecified optical wavelength range, into a respective electrical datasignal having an RF frequency within the same specified RF frequencyrange within which the space based subsystem is configured to transmit aplurality of RF service downlink beams. These N optical signals beingconverted include the other one of the optical signals of each of the Nseparate pairs of optical signals produced by the splitting at step1106. Step 1109, which is similar to step 706 discussed above withreference to FIG. 7, can be performed by the PDs 308 discussed abovewith reference to FIG. 9A.

Step 1111 involves producing, in dependence on the electrical datasignals, the plurality of RF service downlink beams within the specifiedRF frequency range. Step 1111, which is similar to step 708 discussedabove with reference to FIG. 7, can be performed, e.g., by the filters310, LNAs 312, splitters 314, HPAs 318, HFs 320, OMJs 324, and feedhorns 326 discussed above with reference to FIG. 9A.

Step 1113 involves transmitting the plurality of RF service downlinkbeams within the specified RF frequency range. Step 1113, which issimilar to step 710 discussed above with reference to FIG. 7, can beperformed by the feed horns 326 and reflector(s) discussed above withreference to FIG. 9A, and more generally, antenna systems. In accordancewith certain embodiments, because the RF frequencies of the electricaldata signals resulting from the converting (at step 1109) are within thesame specified RF frequency range within which the space based subsystemis configured to transmit the plurality of RF service downlink beams (atstep 1113), there is an elimination of any need for any space basedsubsystem (e.g., 300 and 900A) to perform any frequency conversions whenproducing the plurality of RF service downlink beams in dependence onthe optical feeder uplink beam. In accordance with certain embodiments,the specified RF frequency range within which the satellite (e.g., 100)is configured to produce and transmit a plurality of RF service downlinkbeams is a downlink portion of the Ka band. The downlink portion of theKa band can be from 17.7 GHz to 20.2 GHz, and thus, have a bandwidth of2.5 GHz. Alternatively, the downlink portion of the Ka band can be from17.3 GHz to 20.2 GHz, and thus, have a bandwidth of 2.9 GHz. These arejust a few examples, which are not intended to be all encompassing.

In certain embodiments, step 1106 can be eliminated, in which case steps1109, 1111 and 1113 can also be eliminated. In other words, as notedabove, some or all of the beam splitters 932 shown in FIG. 9A can beeliminated. In other embodiments, step 1106 can involve only splitting asubset of the optical signals produced at step 1104. In other words, ifonly some of the splitters 932 are eliminated, then step 1106 caninvolve splitting only a subset of the N separate optical signals into arespective pair of optical signals, and the downstream steps shown inFIG. 11A would be adjusted accordingly. Further, as explained above withreference to FIGS. 9C and 9D, one or more of the optical signals thatresult from step 1104 can be converted to electrical signals using oneor more photodetectors and such electrical signal(s) can be provided toand consumed by equipment that is located on the satellite, such as acommand and data handling (C&DH) system, an RF communication payload,and one or more digital payloads, but not limited thereto. Also, asexplained above with reference to FIG. 9D, switching of optical signalscan be performed, e.g., using the optical cross-connect switch, tocontrol which signals are included in an optical ISL beam, which signalsare converted to RF service downlink beams, and/or which signals areconverted to electrical signals that are provided to and consumed by(e.g., used to control or otherwise used by) equipment located on thesatellite.

FIG. 11B is a high level flow diagram that is used to summarize methodsfor enabling a space based subsystem of a satellite (e.g., 100) toproduce to an optical inter-satellite link (ISL) beam (e.g., 162) and RFservice downlink beams (e.g., 106 d, 110 d, 114 d), based on an opticalISL beam (e.g., 152) received from another satellite (e.g., 150),according to another embodiment of the present technology. The steps ofFIG. 11B can be performed, e.g., using the components shown in FIG. 9Bdiscussed above.

Steps 1102 and 1104 in FIG. 11B are the same as steps 1102 and 1104 inFIG. 11A, and thus, details of these steps need not be repeated. Adifference between the methods described with reference to FIG. 11A andthe methods described with reference to FIG. 11B is the splitting of theN optical signals that took place in step 1106 of FIG. 11A do not takeplace in FIG. 11B. Rather, in the embodiment of FIG. 11B, a first subsetof the N optical signals (produced at step 1104) are multiplexed at step1108′, and a second subset of the N optical signals (produced at step1104) are converted to electrical data signals at step 1109′.

More specifically, step 1108′ involves multiplexing a first subset ofthe N optical signals that each have a different peak wavelength withina specified optical wavelength range to thereby produce a wavelengthdivision multiplexed optical signal that includes data that is to beforwarded to a further satellite so that the further satellite cantransmit, in dependence thereon, a plurality of RF service downlinkbeams. Step 1108′ can be performed by the WDM multiplexer 936 describedabove with reference to FIG. 9B. As can be appreciated from FIG. 9B, thefirst subset of N optical signals may be filtered (e.g., using thefilters 934_1 to 934_125) before they are multiplexed at step 1108′.

Steps 1110′ and 1112′ in FIG. 11B are similar to steps 1110 and 1112described above with reference to FIG. 11A, except that the optical ISLbeam produced at step 1110′ (and transmitted at step 1112′) is onlyproduced based on the first subset of the N optical signals that aremultiplexed at step 1108′. Steps 1111′ and 1113′ in FIG. 11B are similarto steps 1111 and 1113 described above with reference to FIG. 11A, andthus details thereof need not be described again. Additional details ofsteps 1110′, 1112′, 1111′ and 1113′ can be appreciated from the abovediscussion of FIG. 9B. More generally, additional details of the methodsof FIGS. 11A and 11B can be appreciated from the above discussion of thespace segment equipment described with reference to FIGS. 9A and 9B, aswell as other Figures described above.

Further, as explained above with reference to FIGS. 9C and 9D, a thirdsubset of the optical signals that result from step 1104 can beconverted to electrical signals using one or more photodetectors andsuch electrical signal(s) can be provided to and consumed by equipmentthat is located on the satellite, such as a command and data handling(C&DH) system, an RF communication payload, and one or more digitalpayloads, but not limited thereto. Also, as explained above withreference to FIG. 9D, switching of optical signals can be performed,e.g., using the optical cross-connect switch, to control which signalsare included in an optical ISL beam, which signals are converted to RFservice downlink beams, and/or which signals are converted to electricalsignals that are provided to and consumed by (e.g., used to control orotherwise used by) equipment located on the satellite. In other words,which optical signals make up the first subset, the second subset andthe third subset can be changed over time using optical switching.

RF-to-Optical Space Segment Forward ISL Equipment

FIG. 12A will now be used to describe a portion of space segment forwardISL equipment 1200A, according to an embodiment of the presenttechnology. Such space segment forward ISL equipment 1200A, which canalso be referred to as a satellite ISL link subsystem 1200A, or moregenerally, as a communication subsystem, is configured to receive an RFfeeder uplink beam that is transmitted from a ground based gateway(e.g., 105) to the satellite (e.g., 100) that is carrying the spacesegment forward ISL equipment 1200A, and produce and transmit an opticalISL beam to another satellite (e.g., 150). The other satellite (e.g.,150), to which the optical ISL beam is transmitted, can be carrying thespace segment forward link equipment 300 (described above with referenceto FIG. 3), the space segment ISL equipment 900A (described above withreference to FIG. 9A), or the space segment ISL equipment 900B(described above with reference to FIG. 9B), but is not limited thereto.

Referring to FIG. 12A, the space segment forward ISL equipment 1200A isshown as including a feed horn 1202, an OMJ 1204, TCs 1206_1 and 1206_2,PFs 1208_1 and 1208_2, filters 1212_1 and 1212_2, OEMs 1216_1 and1216_2, WDM multiplexer 1218, OA 1230 and transmitter optics 1240. Thespace segment forward ISL equipment 1200A is also shown as includinglocal oscillators 1222_1 (LO1) and 1222_2 (LO2), which output respectiveRF signals. Additionally, the space segment forward ISL equipment 1200Ais shown as including lasers 1224_1 and 1224_2, each of which isoperable to emit light having a respective different peak opticalwavelength.

The feed horn 1202, along with a reflector (now shown in the Figure),gathers and focuses radio waves of an RF feeder uplink beam (e.g., 106u) and converts it to an RF signal that is provided to the OMJ 1204. Thefeed horn 1202 and the rest of the antenna can be collectively referredto as the antenna or antenna system. In other words, an antenna, as theterm is used herein, can include a feed horn. It is also possible thatthe antenna is a phased array or a lens antenna. The OMJ 1204 separatesthe RF signal into a right hand circular polarization (RHCP) RF signaland a left hand circular polarization (LHCP) RF signal. The OMJ 1204 canalternatively separate the RF signal it receives into a horizontallinear polarization RF signal and vertical linear polarization RFsignal. Each of the TCs 1206_1 and 1206_2 can be used for powermonitoring, payload testing and/or performing calibrations based onsignals passing therethrough. Each of the PFs 1208_1 and 1208_2 (e.g.,bandpass filters) can be used to remove unwanted frequency componentsand/or enhance desired frequency components. For an example, each of thePFs 1208_1 and 1208_2 can pass frequencies within the range of 29.5-30.0GHz, but are not limited thereto. Each of the LNAs 1210_1 and 1210_2amplifies the relatively low-power RF signal it receives from arespective one of the PFs 1208_1 and 1208_2 without significantlydegrading the signals signal-to-noise ratio. The amplified RF signalthat is output by each of the LNAs 1210_1 and 1210_2 is provided to arespective filter 1212_1 and 1212_2.

Each of the filters 1212_1 and 1212_2 allows frequencies to pass withintwo of the colors a, b, c and d. For example, the filter 1212_1 passesfrequencies within the colors a and b, and the filter 412_2 passes thefrequencies within the colors c and d. In accordance with an embodiment:color ‘a’ represents a first sub-band (e.g., 29.50-29.75 GHz) of anallocated uplink frequency band (e.g., 29.50-30.00 GHz) with aright-hand circular polarization (RHCP); color ‘b’ represents a secondsub-band (29.75-30.00 GHz) of the allocated uplink frequency band withRHCP; color ‘c’ represents the first sub-band (e.g., 29.50-29.75 GHz) ofthe allocated uplink frequency band with a left-hand circularpolarization (LHCP); and color ‘d’ represents the second sub-band(29.75-30.00 GHz) of the allocated uplink frequency band with LHCP. Inother embodiments, the colors may include other allocations of thefrequency band and polarization. For example, the polarizations can behorizontal and vertical linear polarizations, rather than RHCP and LHCP.The RF signals that are output from the filters 1212_1 and 1212_2, whichcan be referred to as data modulated RF signals, are provided to EOMs1216_1 and 1216_2, as shown in FIG. 12A.

Still referring to FIG. 12A, the local oscillators (LOs) 1222_1 and1222_2 each produce a different RF carrier signal within the portion ofthe Ka band that is available for transmitting service downlink beams(also referred to as downlink user beams). For example, the LO 1222_1may produce an RF carrier within the RF frequency range from 17.7-18.95GHz (e.g., at 18.325 GHz, but not limited thereto), and the LO 1222_2may produce an RF carrier within the RF frequency range from 18.95-20.2GHz (e.g., at 19.575, but not limited thereto). For another example, theLO 1222_1 may produce an RF carrier within the RF frequency range from17.3-18.75 GHz (e.g., at 18.025 GHz, but not limited thereto), and theLO 1222_2 may produce an RF carrier within the RF frequency range from18.75-20.2 GHz (e.g., at 19.475, but not limited thereto). The RFcarrier signal produced by the LO 1222_1 is used to drive the laser1224_1, and the RF carrier signal produced by the LO 1222_2 is used todrive the laser 1224_2. Each of the lasers 1224_1 and 1224_2 is operableto emit light of a different peak wavelength than the other in responseto being driven by the RF carrier signal output by a respective one ofthe LOs 1222_1 and 1222_2. Infrared (IR), visible or other opticalwavelengths can be produced by the lasers 1224_1 and 1224_2 and used forproducing the optical ISL beams.

Still referring to FIG. 12A, the light emitted by each of the lasers1224_1 and 1224_2, which can be referred to as an optical carriersignal, is provided (e.g., via a respective optical fiber) to arespective one of the EOMs 1216_1 and 1216_2. Each of the EOMs 1216_1and 1216_2 is an optical device in which a signal-controlled elementexhibiting an electro-optic effect is used to modulate a respective beamof light. The EOM 1216_1 also receives the RF signal output by thefilter 1212_1, and the EOM 1216_2 also receives the RF signal output bythe filter 1212_2. The modulation performed by the EOMs 1216_1 and1216_2 may be imposed on the phase, frequency, amplitude, orpolarization of a beam of light, or any combination thereof. Inaccordance with a specific embodiment, each of the EOMs 1216_1 and1216_2 is a phase modulating EOM that is used as an amplitude modulatorby using a Mach-Zehnder interferometer. In other words, each of the EOMs1216_1 and 1216_2 can be implemented as a Mach-Zehnder modulator (MZM),which can be a Lithium Niobate Mach-Zehnder modulator, but is notlimited thereto. In accordance with specific embodiments, each of theEOMs 1216_1 and 1216_2 is implemented as an MZM that produces anamplitude modulated (AM) optical waveform with a modulation indexbetween 10% and 80% in order to maintain fidelity of an RF waveform(modulated therein) without too much distortion. The optical signal thatis output by each of the EOMs 1216_1 and 1216_2 can be referred to as anoptical data signal. The modulation scheme that is implemented by theEOMs 204 can result in double- or vestigial-sidebands, including both anupper sideband (USB) and a lower sideband (LSB). Alternativelysingle-sideband modulation (SSB) can be utilized to increase bandwidthand transmission power efficiency.

Explained another way, each of the EOMs 1216_1 and 1216_2 is configuredto receive an LO modulated optical carrier signal from a respective oneof the lasers 1224_1 and 1224_2 and receive a different data modulatedRF signal including data (e.g., corresponding to at least one of aplurality of RF service downlink beams). Additionally, each of the EOMs1216_1 and 1216_2 is configured to output an optical data signalcarrying data and including the LO frequency signal required to generatea frequency converted RF signal (e.g., corresponding to at least one ofa plurality of RF service downlink beams) and having an RF frequencywithin the same specified RF frequency range within which anothersatellite (e.g., 150), to which an optical ISL beam (that will be outputby the transmitter optics 1240) is being transmitted, is configured totransmit a plurality of RF service downlink beams.

The two optical data signals that are output by the EOMs 1216_1 and1216_2 are provided to the WDM MUX 1218, which can also be referred toas a dense wavelength division multiplexing (DWDM) MUX. The WMD MUX 1218multiplexes (i.e., combines) the two optical data signals, received fromthe two EOMs 1216_1 and 1216_2, onto a single optical fiber, with eachof the two optical data signals being carried at the same time on itsown separate optical wavelength within an optical frequency range (e.g.,from 1510 nm to 1560 nm, but not limited thereto).

The signal that is output by the WMD MUX 1218, which can be referred toas a wavelength division multiplexed optical ISL signal, is provided tothe optical amplifier (OA) 1230. The OA 1230 amplifies the wavelengthdivision multiplexed optical ISL signal so that the wavelength divisionmultiplexed optical ISL signal has sufficient power to enabletransmission thereof from the satellite (e.g., 100) in space to anothersatellite (e.g., 150) in space. The OA 1230 can be an erbium-doped fiberamplifier (EDFA), but is not limited thereto. The output of the OA 1230can be referred to as an optically amplified wavelength divisionmultiplexed optical ISL signal.

The optically amplified wavelength division multiplexed optical ISLsignal, which is output by the OA 1230, is provided (e.g., via anoptical fiber) to the transmitter optics 1240. The transmitter optics1240, which can also be referred to as a telescope, can includes opticalelements such as lenses, mirrors, reflectors, filters and/or the like.The transmitter optics 1240 outputs a collimated optical ISL beam thatis aimed at another satellite. A gimbal, and/or the like, can be used tocontrol the steering of the transmitter optics 1240. The diameter of thetransmitter optics 1240 can depend on the distance between satellitesand whether the optical ISL beam terminates in the adjacent satellite orif it continues on to another satellite. The diameter of the transmitteroptics 1240 can nominally range from about 5 to 15 cm. If the opticalISL beam continues on to adjacent satellites the diameter may need to bebigger in order to account for compiling SNR from traversing multiplelinks.

FIG. 12A also shows that one or more digital payloads 1242 (labeled1242_1 . . . 1242_n) can provide optical data signals to the WDM MUX1218 so that information obtained by or otherwise provided by thedigital payload(s) 1242 can be included in the optical ISL beam that istransmitted to another satellite, which can eventually (that that othersatellite, or a further satellite) be included in an optical feederdownlink that is transmitted to a ground based optical gateway.Exemplary types of digital payloads include imaging and/or weatherpayloads, but are not limited thereto.

FIG. 12B depicts RF-to-optical space segment inter-satellite link (ISL)equipment, according to another embodiment of the present technology.All the elements that are shown in FIG. 12B to the left of and includingthe EOMs 1216_1 and 1216_2 are the same as in FIG. 12A, and thus neednot be described again. In FIG. 12B, rather than the combining the twooptical data signals that are output by the EOMs 1216_1 and 1216_2(using a WDM MUX 1218), each of the optical data signals is provided toa respective OA 1230_1 and 1230_2, and the output of the OA 1230_1 isprovided (e.g., via an optical fiber) to the transmitter optics 1240_1,and the output of the OA 1230_2 is provided (e.g., via an optical fiber)to the transmitter optics 1240_2. Each of the transmitter optics 1240_1outputs a collimated optical ISL beam that is aimed at another satellite(e.g., 150), and the transmitter optics 1240_2 outputs a furthercollimated optical ISL beam that is aimed at a further satellite (e.g.,160). In other words, in the embodiment of FIG. 12B, two differentoptical ISL beams that are aimed at different satellites (e.g., 150 and160) can be generated from one RF feeder uplink beam received by asatellite (e.g., 100).

FIG. 12C depicts RF-to-optical space segment inter-satellite link (ISL)equipment, according to a further embodiment of the present technology.Elements that are shown in FIG. 12B to the left of and including theEOMs 1216_1 and 1216_2 are the same as in FIGS. 12A and 12B, and thusneed not be described again. In FIG. 12C, beam splitter (BS) 1217_1 isconnected to the output of the EOM 1216_1, and BS 1217_2 is connected tothe output of the EOM 1216_2. Each BS 1217 splits the optical datasignal it receives into two optical data signals, which include the samedata, but may have different power, depending upon how the BS isimplemented. Unless stated otherwise, it will be assumed that each BS1217 splits the optical data signal it receives into two optical datasignals having the same content and power (i.e., two substantiallyidentical optical data signals). The two optical data signals that areoutput by each BS 1217 is shown as being provided to the opticalcross-connect switch 1220.

FIG. 12C also shows that one or more digital payloads 1242 (labeled1242_1 . . . 1242_n) can provide optical data signals to the opticalcross-connect switch 1220. Exemplary types of digital payloads includeimaging and/or weather payloads, but are not limited thereto. A firstsubset of the outputs of the optical cross-connect switch 1220 isconnected to a WDM MUX 1222_1, and a second subset of the outputs of theoptical cross-connect switch 1220 is connected to a WDM MUX 1222_2. Thesignal that is output by the WMD MUX 1222_1, which can be referred to asa first wavelength division multiplexed optical ISL signal, is providedto the optical amplifier (OA) 1230_1. The OA 1230_1 amplifies the firstwavelength division multiplexed optical ISL signal so that thewavelength division multiplexed optical ISL signal has sufficient powerto enable transmission thereof from the satellite (e.g., 100) in spaceto another satellite (e.g., 150) in space. The signal that is output bythe WMD MUX 1222_2, which can be referred to as a second wavelengthdivision multiplexed optical ISL signal, is provided to the opticalamplifier (OA) 1230_2. The OA 1230_2 amplifies the wavelength divisionmultiplexed optical ISL signal so that the wavelength divisionmultiplexed optical ISL signal has sufficient power to enabletransmission thereof from the satellite (e.g., 100) in space to anothersatellite (e.g., 160) in space.

The optically amplified wavelength division multiplexed optical ISLsignals, which are output by the OAs 1230_1 and 1230_2, are provided(e.g., via an optical fiber) respectively to the transmitter optics1240_1 and 1240_2. The transmitter optics 1240_1 outputs a collimatedoptical ISL beam that is aimed at another satellite (e.g., 150), and thetransmitter optics 1240_2 outputs a collimated optical ISL beam that isaimed at a further satellite (e.g., 160).

The BSs 1217 enable the same optical data signals to be included in morethan one of the ISL beams, e.g., to provide for redundancy and/orbroadcast capabilities. If such capabilities are not wanted or needed,the BSs 1217 can be eliminated.

The optical cross-connect switch 1220 enables the sources of the opticaldata included in the different ISL beams to be changed over time, asdesired. If such capabilities are not wanted or needed, the opticalcross-connect switch 1220 can be eliminated.

Methods for Producing ISL Beam(s) Based on an RF Feeder Uplink Beam

FIG. 13A is a high level flow diagram that is used to summarize methodsfor enabling a space based subsystem of a satellite (e.g., 100) toproduce to an optical inter-satellite link (ISL) beam (e.g., 152), basedon an RF feeder uplink beam (e.g., 102 u) received from a ground basedgateway (e.g., 105), according to certain embodiments of the presenttechnology. The steps of FIG. 13A can be performed, e.g., using thecomponents shown in FIG. 12A discussed above. The optical ISL beam canbe transmitted from the satellite (e.g., 100) to another satellite(e.g., 150).

Referring to FIG. 13A, step 1302 involves receiving an RF feeder uplinkbeam (e.g., 102 u) from a ground based subsystem, which can be a groundbased gateway, and in dependence thereon producing an RF signal. Step1302 can be performed by an antenna that includes the feed horn 1202shown in FIG. 12A.

Step 1304 involves separating the RF signal into a first RF data signalhaving a first polarization and a second RF data signal having a secondpolarization that is different than the first polarization. The firstpolarization can be one of right hand circular polarization (RHCP) orleft hand circular polarization (LHCP), and the second polarization theother one of RHCP or LHCP. Alternatively, the first polarization can beone of vertical or horizontal linear polarization, and the secondpolarization the other one of vertical or horizontal linearpolarization. Step 1304 can be performed using the OMJ 1204 in FIG. 12A.

Step 1306 involves producing first and second RF carrier signals havingrespective first and second RF frequencies. Step 1306 can be performedby the local oscillators 1222_1 and 1222_2 in FIG. 12A.

Step 1308 involves driving first and second lasers with the first andsecond RF carrier signals to thereby emit respective first and secondoptical carrier signals having different peak wavelengths within aspecified optical wavelength range, wherein the first optical carriersignal has the first RF frequency, and the second optical carrier signalhas the second RF frequency. Step 1308 can be performed using the lasers1224_1 and 1224_2 in FIG. 12A.

Step 1310 involves electro-optically modulating the first RF data signalwith the first optical carrier signal to thereby produce a first opticaldata signal, and electro-optically modulating the second RF data signalwith the second optical carrier signal to thereby produce a secondoptical data signal. Step 1310 can be performed by the EOMs 1216_1 and1216_2 in FIG. 12A. Further, it is noted that the first and second RFdata signals can be amplified and filtered before step 1310 isperformed. Such amplification and filtering can be performed by thepreselect filters 1208_1 and 1208_2, the LNAs 1210_1 and 1210_2, and thefilters 1212_1 and 1212_2 in FIG. 12B.

Step 1312 involves multiplexing the first and second optical datasignals to thereby produce a wavelength division multiplexed opticalsignal. Step 1312 can be performed by the WDM multiplexer 1218 in FIG.12A.

Step 1314 involves producing an optical ISL beam in dependence on thewavelength division multiplexed optical signal, and step 1316 involvestransmitting the optical ISL beam to another satellite. Steps 1314 and1316 can be performed by the transmitter optics 1240 in FIG. 12A.

In accordance with certain embodiments, the RF frequencies of the firstand second optical data signals produced by the electro-opticallymodulating are within the same specified RF frequency range within whichthe other satellite is configured to transmit a plurality of RF servicedownlink beams, thereby eliminating any need for the other satellite toperform any frequency conversions when producing the plurality of RFservice downlink beams in dependence on the optical ISL beam. Inaccordance with certain embodiments, the specified RF frequency rangewithin which the other satellite (e.g., 150) is configured to produceand transmit RF service downlink beams is a downlink portion of the Kaband. The downlink portion of the Ka band can be from 17.7 GHz to 20.2GHz, and thus, have a bandwidth of 2.5 GHz. Alternatively, the downlinkportion of the Ka band can be from 17.3 GHz to 20.2 GHz, and thus, havea bandwidth of 2.9 GHz. These are just a few examples, which are notintended to be all encompassing.

In accordance with certain embodiments, additionally optical datasignals, e.g., received from one or more digital payloads (e.g., thoselabeled 1242_1 . . . 1242_n in FIG. 12A) can also be multiplexed andthereby included in the wavelength division multiplexed optical signalproduced at step 1312.

FIG. 13B is a high level flow diagram that is used to summarize methodsfor enabling a space based subsystem of a satellite (e.g., 100) toproduce to two optical ISL beams (e.g., 152 and 162), based on an RFfeeder uplink beam (e.g., 102 u) received from a ground based gateway(e.g., 105), according to certain embodiments of the present technology.The steps of FIG. 13B can be performed, e.g., using the components shownin FIG. 12B discussed above. The two optical ISL beams can betransmitted from the satellite (e.g., 100) to two other satellites(e.g., 150 and 160).

Steps 1302, 1304, 1306, 1308 and 1310 in FIG. 13B are the same as steps1302, 1304, 1306, 1308 and 1310 in FIG. 13A, and thus, details of thesesteps need not be repeated. A difference between the methods describedwith reference to FIG. 13A and the methods described with reference toFIG. 13B is the multiplexing that took place at step 1312 in FIG. 13Adoes not take place in FIG. 13B. Rather, in the embodiment of FIG. 13B,the first and second optical data signals produced at step 1310 are eachused to produce a separate optical ISL beam. More specifically,referring to FIG. 13B, step 1314′ involves producing a first optical ISLbeam in dependence on the first optical data signal, and producing asecond optical ISL beam in dependence on the second optical data signal,and step 1316′ involves transmitting the first optical ISL beam to afirst other satellite and transmitting the second optical ISL beam to asecond other satellite. Steps 1314′ and 1316′ can be performed using thetransmitter optics 1240_1 and 1240_2 in FIG. 12B, as can be appreciatedfrom the above discussion thereof.

In accordance with certain embodiments, two copies of each of opticaldata signals that are produced at step 1310 can be formed by splittingeach optical data signal into two, e.g., using the beam splitters 1217discussed above with reference to FIG. 12C. Further, optical switchingand WDM multiplexing can take place prior to step 1316′, so that thecontents of each of the first and second optical ISL beams transmittedat step 1316′ can be changed as desired, as was also described abovewith reference to FIG. 12C. Further, as was also described above withreference to FIG. 12C, optical data signals from one or more datapayloads produced by or otherwise provided by one or more digitalpayloads can also be included in one or more of the optical ISLs, ifdesired. Further variations to the methods summarized with reference toFIGS. 13A and 13B can be appreciated from the above discussion of FIGS.12A and 12B.

Note that the discussion above introduces many different features andmany embodiments. It is to be understood that the above-describedembodiments are not all mutually exclusive. That is, the featuresdescribed above (even when described separately) can be combined in oneor multiple embodiments.

Certain embodiments of the present technology are directed to a groundbased subsystem for inclusion in an optical gateway and for use intransmitting an optical feeder uplink beam to a satellite that isconfigured to receive the optical feeder uplink beam. In accordance withan embodiment, the ground based subsystem includes a wavelength-divisionmultiplexing (WDM) multiplexer, and optical amplifier and transmitteroptics. The WDM multiplexer is configured to receive one or more opticaldata signals from one or more optical networks that are external to theground based optical gateway, and combine the one or more optical datasignals into a wavelength division multiplexed optical signal. Theoptical amplifier is configured to amplify the wavelength divisionmultiplexed optical signal to thereby produce an optically amplifiedwavelength division multiplexed optical signal. The transmitter opticsis/are configured to receive the optically amplified wavelength divisionmultiplexed optical signal and transmit an optical feeder uplink beam tothe satellite in dependence thereon. In accordance with certainembodiments, the ground based optical gateway does not perform anymodulation of, and does not perform any demodulation of, the one or moreoptical data signals that are received from the one or more opticalnetworks that are external to the ground based optical gateway beforethey are provided to the WDM multiplexer.

In accordance with certain embodiments, the ground based subsystemfurther includes one or more wavelength converters each of which isconfigured to convert a peak optical wavelength of one of the one ormore optical data signals, received from the one or more opticalnetworks that are external to the ground based optical gateway, to adifferent peak optical wavelength so that no two optical signalsreceived at different inputs of the WDM multiplexer have a same peakoptical wavelength. In accordance with certain embodiments, the groundbased subsystem additionally, or alternatively, includes one or morefrequency converters each of which is configured to one or up-convert ordown-convert a frequency of a different one of the optical signals beingprovided to the WDM multiplexer from one of the one or more opticalnetworks that are external to the ground based optical gateway, tothereby eliminate any need for frequency conversion to be performed onthe satellite to which the optical feeder uplink beam is beingtransmitted.

In accordance with certain embodiments, the ground based subsystemfurther includes a plurality of lasers and a plurality ofelectro-optical modulators (EOMs). Each of the plurality of lasers isoperable to emit an optical signal having a different peak wavelengthwithin a specified optical wavelength range. Each of the EOMs isconfigured to receive an optical signal from a respective one of theplurality of lasers, receive a different data modulated RF carriersignal that has been modulated to carry data for at least one of aplurality of RF service downlink beams. In such embodiments, the WDMmultiplexer can also be configured to receive the optical data signalsoutput by the plurality of EOMs, and combine the plurality of opticaldata signals received from the plurality of EOMs with one another andwith the one or more optical data signals that are received from the oneor more optical networks that are external to the ground based opticalgateway into the wavelength division multiplexed optical signal, thatafter being amplified by the optical amplifier, is transmitted by thetransmitter optics to a satellite in the optical feeder uplink beam. Theground based subsystem can also include a plurality of RF modulatorsconfigured to produce the data modulated RF carrier signals that arereceived by the plurality of EOMs, wherein each of the RF modulatorsreceives an RF carrier signal having an RF frequency within the samespecified RF frequency range within which the satellite is configured totransmit the plurality of RF service downlink beams. The ground basedsubsystem of claim 5, can also include one or more oscillatorsconfigured to produce the RF carrier signals that are provided to the RFmodulators, each of the RF carriers signals having an RF frequencywithin the same specified RF frequency range within which the satelliteis configured to transmit the plurality of RF service downlink beams.

Certain embodiments of the present technology are directed a method forenabling a ground based optical gateway to produce and transmit anoptical feeder uplink beam to a satellite that is configured to receivethe optical feeder uplink beam. In accordance with an embodiment, themethod, which is for use by the ground based optical gateway, includes:receiving one or more optical data signals from one or more opticalnetworks that are external to the ground based optical gateway;multiplexing the one or more optical data signals, received from the oneor more optical networks that are external to the ground based opticalgateway, to thereby produce a wavelength division multiplexed opticalsignal; producing an optical feeder uplink beam, in dependence on thewavelength division multiplexed optical signal; and transmitting theoptical feeder uplink beam through free-space to the satellite. Inaccordance with certain embodiments, the ground based optical gatewaydoes not perform any modulation of, and does not perform anydemodulation of, the one or more optical data signals that are receivedfrom the one or more optical networks that are external to the groundbased optical gateway before they are multiplexed to produce thewavelength division multiplexed optical signal.

The method can also include: emitting a plurality of optical signalseach having a different peak wavelength that is within a specifiedoptical wavelength range; and electro-optically modulating each of theoptical signals with one of a plurality of different data modulated RFcarrier signals, each of which has been modulated to carry data for atleast one of the plurality of RF service downlink beams, to therebyproduce a plurality of optical data signals. In accordance with certainembodiments, the multiplexing includes multiplexing the plurality ofoptical data signals, produced as a result of the electro-opticallymodulating, with the optical data signals received from the one or moreoptical networks that are external to the ground based optical gatewayto thereby produce into the wavelength division multiplexed opticalsignal.

The method can also include converting a peak optical wavelength of atleast one of the one or more optical data signals, received from the oneor more optical networks that are external to the ground based opticalgateway, to a different peak optical wavelength so that no two opticalsignals that are multiplexed to produced wavelength division multiplexedoptical signal have a same peak optical wavelength.

The method can also include up-converting or down-converting a frequencyof at least one of the one or more optical data signals, received fromthe one or more optical networks that are external to the ground basedoptical gateway, to thereby eliminate any need for frequency conversionto be performed on the satellite to which the optical feeder uplink beamis being transmitted.

Certain embodiments of the present technology are directed to a groundbased subsystem for inclusion in an optical gateway and for use inreceiving an optical feeder downlink beam from a satellite. Inaccordance with an embodiment, the ground based subsystem includesreceiver optics, an optical amplifier and a WDM multiplexer. Thereceiver optics is/are configured to receive a wavelength divisionmultiplexed optical feeder downlink beam from a satellite. The opticalamplifier is configured to amplify the wavelength division multiplexedoptical signal received by the amplifier from the receiver optics. TheWDM demultiplexer is configured to receive an amplified wavelengthdivision multiplexed optical signal from the amplifier and separate theamplified wavelength division multiplexed optical signal into aplurality of separate optical signals, each of which has a differentpeak wavelength. In accordance with certain embodiments, one or more ofthe optical data signals that are output by the WDM demultiplexer areprovided to one or more optical networks that are external to the groundbased optical gateway without the optical gateway performing anydemodulation of, and without the optical gateway performing anymodulation of, the one or more optical data signals that are provided tothe one or more optical networks that are external to the ground basedoptical gateway.

The ground based subsystem can also include one or more wavelengthconverters each of which is configured to convert a peak opticalwavelength of one of the one or more optical data signals, that is beingprovided to one of the one or more optical networks that are external tothe ground based optical gateway, to a different peak optical wavelengthbefore the one of the one or more optical data signals is provided tothe one of the one or more optical networks that are external to theground based optical gateway. Additionally, or alternatively, the groundbased subsystem can also include one or more frequency converters eachof which is configured to one of up-convert or down-convert a frequencyof at least one of the one or more optical data signals, that is beingprovided to one of the one or more optical networks that are external tothe ground based optical gateway, before the one of the one or moreoptical data signals is provided to the one of the one or more opticalnetworks that are external to the ground based optical gateway.

In accordance with certain embodiments, the ground based subsystemfurther includes a plurality of photodetectors, each of which converts adifferent one of a subset of the optical signals that are output fromthe WDM demultiplexer, to a respective electrical data signal. Incertain such embodiments, the subset of the optical signals that areconverted to electrical data signals by the plurality of photodetectorsdo not include the one or more of the optical data signals that, afterbeing output by the WDM demultiplexer, are provided to one or moreoptical networks that are external to the ground based optical gateway.

Certain embodiments of the present technology are directed a method foruse by a ground based optical gateway. In accordance with an embodiment,the method includes: receiving a wavelength division multiplexed opticalfeeder downlink beam from a satellite; amplifying the wavelengthdivision multiplexed optical signal; demultiplexing the amplifiedwavelength division multiplexed optical signal to thereby separate theamplified wavelength division multiplexed optical signal into aplurality of optical signals, each of which has a different peakwavelength; and providing one or more of the optical data signals thatare output by the WDM demultiplexer to one or more optical networks thatare external to the ground based optical gateway without the opticalgateway performing any modulation of, and without the optical gatewayperforming any demodulation of, the one or more optical data signalsthat are provided to the one or more optical networks that are externalto the ground based optical gateway.

The method can also include converting a peak optical wavelength of atleast one of the one or more optical data signals, that is beingprovided to one of the one or more optical networks that are external tothe ground based optical gateway, to a different peak optical wavelengthbefore the at least one of the one or more optical data signals isprovided to the one of the one or more optical networks that areexternal to the ground based optical gateway. Additionally, oralternatively, the method can include up-converting or down-converting afrequency of at least one of the one or more optical data signals, thatis being provided to one of the one or more optical networks that areexternal to the ground based optical gateway, before the at least one ofthe one or more optical data signals is provided to the one of the oneor more optical networks that are external to the ground based opticalgateway.

In accordance with certain embodiments, the method further includesconverting at subset of the optical signals that result from thedemultiplexing to respective electrical data signals. In some suchembodiments, the subset of the optical signals that are converted toelectrical data signals do not include the one or more of the opticaldata signals that are provided to one or more optical networks that areexternal to the ground based optical gateway without the optical gatewayperforming any modulation and without the optical gateway performing anydemodulation thereof.

For purposes of this document, it should be noted that the dimensions ofthe various features depicted in the figures may not necessarily bedrawn to scale.

For purposes of this document, reference in the specification to “anembodiment,” “one embodiment,” “some embodiments,” or “anotherembodiment” may be used to describe different embodiments or the sameembodiment.

For purposes of this document, a connection may be a direct connectionor an indirect connection (e.g., via one or more others parts). In somecases, when an element is referred to as being connected or coupled toanother element, the element may be directly connected to the otherelement or indirectly connected to the other element via interveningelements. When an element is referred to as being directly connected toanother element, then there are no intervening elements between theelement and the other element. Two devices are “in communication” ifthey are directly or indirectly connected so that they can communicateelectronic signals between them.

For purposes of this document, the term “based on” may be read as “basedat least in part on.”

For purposes of this document, without additional context, use ofnumerical terms such as a “first” object, a “second” object, and a“third” object may not imply an ordering of objects, but may instead beused for identification purposes to identify different objects.

For purposes of this document, the term “set” of objects may refer to a“set” of one or more of the objects.

The foregoing detailed description has been presented for purposes ofillustration and description. It is not intended to be exhaustive or tolimit the subject matter claimed herein to the precise form(s)disclosed. Many modifications and variations are possible in light ofthe above teachings. The described embodiments were chosen in order tobest explain the principles of the disclosed technology and itspractical application to thereby enable others skilled in the art tobest utilize the technology in various embodiments and with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of be defined by the claims appended hereto.

1-11. (canceled)
 12. A ground based subsystem for inclusion in anoptical gateway of a satellite communication system and for use inreceiving an optical feeder downlink beam from a satellite of thesatellite communication system, the ground based subsystem comprising:receiver optics configured to receive a wavelength division multiplexedoptical feeder downlink beam from a satellite of the satellitecommunication system; an optical amplifier configured to amplify thewavelength division multiplexed optical signal received by the amplifierfrom the receiver optics; a wavelength-division multiplexing (WDM)demultiplexer configured to receive an amplified wavelength divisionmultiplexed optical signal from the amplifier and separate the amplifiedwavelength division multiplexed optical signal into a plurality ofseparate optical signals, each of which has a different peak wavelength;wherein the ground based subsystem is configured to cause one or more ofthe optical signals that are output by the WDM demultiplexer to beprovided to one or more optical networks that are external to the groundbased optical gateway, within which the ground based subsystem isincluded, without the optical gateway performing any demodulation of,and without the optical gateway performing any modulation of, the one ormore optical signals that are provided to the one or more opticalnetworks that are external to the ground based optical gateway; andfurther comprising one or more wavelength converters each of which isconfigured to convert a peak optical wavelength of one of the one ormore optical signals, that is being provided to one of the one or moreoptical networks that are external to the ground based optical gateway,to a different peak optical wavelength before the one of the one or moreoptical signals is provided to the one of the one or more opticalnetworks that are external to the ground based optical gateway, withoutthe one or more wavelength converters performing any demodulation of,and without the one or more wavelength converters performing anymodulation of, the one or more optical signals that are provided to theone or more optical networks that are external to the ground basedoptical gateway.
 13. A ground based subsystem for inclusion in anoptical gateway of a satellite communication system and for use inreceiving an optical feeder downlink beam from a satellite of thesatellite communication system, the ground based subsystem comprising:receiver optics configured to receive a wavelength division multiplexedoptical feeder downlink beam from a satellite of the satellitecommunication system; an optical amplifier configured to amplify thewavelength division multiplexed optical signal received by the amplifierfrom the receiver optics; a wavelength-division multiplexing (WDM)demultiplexer configured to receive an amplified wavelength divisionmultiplexed optical signal from the amplifier and separate the amplifiedwavelength division multiplexed optical signal into a plurality ofseparate optical signals, each of which has a different peak wavelength;wherein the ground based subsystem is configured to cause one or more ofthe optical signals that are output by the WDM demultiplexer to beprovided to one or more optical networks that are external to the groundbased optical gateway, within which the ground based subsystem isincluded, without the optical gateway performing any demodulation of,and without the optical gateway performing any modulation of, the one ormore optical signals that are provided to the one or more opticalnetworks that are external to the ground based optical gateway; andfurther comprising one or more frequency converters each of which isconfigured to one of up-convert or down-convert a frequency of at leastone of the one or more optical signals, that is being provided to one ofthe one or more optical networks that are external to the ground basedoptical gateway, before the one of the one or more optical signals isprovided to the one of the one or more optical networks that areexternal to the ground based optical gateway, without the one or morefrequency converters performing any demodulation of, and without the oneor more frequency converters performing any modulation of, the one ormore optical signals that are provided to the one or more opticalnetworks that are external to the ground based optical gateway.
 14. Theground based subsystem of claim 12, further comprising: a plurality ofphotodetectors, each of which converts a different one of a subset ofthe optical signals that are output from the WDM demultiplexer, to arespective electrical signal.
 15. A ground based subsystem for inclusionin an optical gateway of a satellite communication system and for use inreceiving an optical feeder downlink beam from a satellite of thesatellite communication system, the ground based subsystem comprising:receiver optics configured to receive a wavelength division multiplexedoptical feeder downlink beam from a satellite of the satellitecommunication system; an optical amplifier configured to amplify thewavelength division multiplexed optical signal received by the amplifierfrom the receiver optics; a wavelength-division multiplexing (WDM)demultiplexer configured to receive an amplified wavelength divisionmultiplexed optical signal from the amplifier and separate the amplifiedwavelength division multiplexed optical signal into a plurality ofseparate optical signals, each of which has a different peak wavelength;a plurality of photodetectors, each of which converts a different one ofa subset of the optical signals that are output from the WDMdemultiplexer, to a respective electrical signal; wherein the groundbased subsystem is configured to cause one or more of the optical datasignals that are output by the WDM demultiplexer to be provided to oneor more optical networks that are external to the ground based opticalgateway, within which the ground based subsystem is included, withoutthe optical gateway performing any demodulation of, and without theoptical gateway performing any modulation of, the one or more opticalsignals that are provided to the one or more optical networks that areexternal to the ground based optical gateway; and wherein the subset ofthe optical signals that are converted to electrical signals by theplurality of photodetectors do not include the one or more of theoptical signals that, after being output by the WDM demultiplexer, areprovided to one or more optical networks that are external to the groundbased optical gateway.
 16. (canceled)
 17. A method for use by a groundbased optical gateway of a satellite communication system, the methodcomprising: receiving a wavelength division multiplexed optical feederdownlink beam from a satellite of the satellite communication system;amplifying the wavelength division multiplexed optical signal;demultiplexing the amplified wavelength division multiplexed opticalsignal, using a WDM demultiplexer within the ground based opticalgateway of the satellite communication system, to thereby separate theamplified wavelength division multiplexed optical signal into aplurality of optical signals, each of which has a different peakwavelength; providing one or more of the optical data signals that areoutput by the WDM demultiplexer, within the ground based optical gatewayof the satellite communication system, to one or more optical networksthat are external to the ground based optical gateway without theoptical gateway performing any modulation of, and without the opticalgateway performing any demodulation of, the one or more optical datasignals that are provided to the one or more optical networks that areexternal to the ground based optical gateway; and converting a peakoptical wavelength of at least one of the one or more optical signals,that is being provided to one of the one or more optical networks thatare external to the ground based optical gateway, to a different peakoptical wavelength before the at least one of the one or more opticalsignals is provided to the one of the one or more optical networks thatare external to the ground based optical gateway; wherein the convertingthe peak optical wavelength of the at least one of the one or moreoptical data signals is performed without performing any demodulationof, and without performing any modulation of, the one or more opticalsignals that are provided to the one or more optical networks that areexternal to the ground based optical gateway.
 18. A method for use by aground based optical gateway of a satellite communication system, themethod comprising: receiving a wavelength division multiplexed opticalfeeder downlink beam from a satellite of the satellite communicationsystem; amplifying the wavelength division multiplexed optical signal;demultiplexing the amplified wavelength division multiplexed opticalsignal, using a WDM demultiplexer within the ground based opticalgateway of the satellite communication system, to thereby separate theamplified wavelength division multiplexed optical signal into aplurality of optical signals, each of which has a different peakwavelength; providing one or more of the optical data signals that areoutput by the WDM demultiplexer, within the ground based optical gatewayof the satellite communication system, to one or more optical networksthat are external to the ground based optical gateway without theoptical gateway performing any modulation of, and without the opticalgateway performing any demodulation of, the one or more optical datasignals that are provided to the one or more optical networks that areexternal to the ground based optical gateway; and up-converting ordown-converting a frequency of at least one of the one or more opticalsignals, that is being provided to one of the one or more opticalnetworks that are external to the ground based optical gateway, beforethe at least one of the one or more optical signals is provided to theone of the one or more optical networks that are external to the groundbased optical gateway; wherein the up-converting or down-converting isperformed without performing any demodulation of, and without performingany modulation of, the one or more optical signals that are provided tothe one or more optical networks that are external to the ground basedoptical gateway.
 19. The method of claim 17, further comprising:converting at least a subset of the optical signals that result from thedemultiplexing to respective electrical signals.
 20. (canceled)
 21. Amethod for use by a ground based optical gateway of a satellitecommunication system, the method comprising: receiving a wavelengthdivision multiplexed optical feeder downlink beam from a satellite ofthe satellite communication system; amplifying the wavelength divisionmultiplexed optical signal; demultiplexing the amplified wavelengthdivision multiplexed optical signal, using a WDM demultiplexer withinthe ground based optical gateway of the satellite communication system,to thereby separate the amplified wavelength division multiplexedoptical signal into a plurality of optical signals, each of which has adifferent peak wavelength; providing one or more of the optical signalsthat are output by the WDM demultiplexer, within the ground basedoptical gateway of the satellite communication system, to one or moreoptical networks that are external to the ground based optical gatewaywithout the optical gateway performing any modulation of, and withoutthe optical gateway performing any demodulation of, the one or moreoptical signals that are provided to the one or more optical networksthat are external to the ground based optical gateway; and converting asubset of the optical signals that result from the demultiplexing torespective electrical signals within the ground based optical gateway;wherein the subset of the optical signals that are converted toelectrical signals within the ground based optical gateway do notinclude the one or more of the optical signals that are provided to oneor more optical networks that are external to the ground based opticalgateway without the optical gateway performing any modulation andwithout the optical gateway performing any demodulation thereof; andconverting a peak optical wavelength of at least one of the one or moreoptical signals, that is being provided to one of the one or moreoptical networks that are external to the ground based optical gateway,to a different peak optical wavelength before the at least one of theone or more optical signals is provided to the one of the one or moreoptical networks that are external to the ground based optical gateway;wherein the converting the peak optical wavelength of the at least oneof the one or more optical data signals is performed without performingany demodulation of, and without performing any modulation of, the oneor more optical signals that are provided to the one or more opticalnetworks that are external to the ground based optical gateway.
 22. Amethod for use by a ground based optical gateway of a satellitecommunication system, the method comprising: receiving a wavelengthdivision multiplexed optical feeder downlink beam from a satellite ofthe satellite communication system; amplifying the wavelength divisionmultiplexed optical signal; demultiplexing the amplified wavelengthdivision multiplexed optical signal, using a WDM demultiplexer withinthe ground based optical gateway of the satellite communication system,to thereby separate the amplified wavelength division multiplexedoptical signal into a plurality of optical signals, each of which has adifferent peak wavelength; providing one or more of the optical signalsthat are output by the WDM demultiplexer, within the ground basedoptical gateway of the satellite communication system, to one or moreoptical networks that are external to the ground based optical gatewaywithout the optical gateway performing any modulation of, and withoutthe optical gateway performing any demodulation of, the one or moreoptical signals that are provided to the one or more optical networksthat are external to the ground based optical gateway; and converting asubset of the optical signals that result from the demultiplexing torespective electrical signals within the ground based optical gateway;wherein the subset of the optical signals that are converted toelectrical signals within the ground based optical gateway do notinclude the one or more of the optical signals that are provided to oneor more optical networks that are external to the ground based opticalgateway without the optical gateway performing any modulation andwithout the optical gateway performing any demodulation thereof; andup-converting or down-converting a frequency of at least one of the oneor more optical signals, that is being provided to one of the one ormore optical networks that are external to the ground based opticalgateway, before the at least one of the one or more optical signals isprovided to the one of the one or more optical networks that areexternal to the ground based optical gateway; wherein the up-convertingor down-converting is performed without performing any demodulation of,and without performing any modulation of, the one or more opticalsignals that are provided to the one or more optical networks that areexternal to the ground based optical gateway.
 23. The ground basedsubsystem of claim 15, further comprising: one or more wavelengthconverters each of which is configured to convert a peak opticalwavelength of one of the one or more optical signals, that is beingprovided to one of the one or more optical networks that are external tothe ground based optical gateway, to a different peak optical wavelengthbefore the one of the one or more optical signals is provided to the oneof the one or more optical networks that are external to the groundbased optical gateway, without the one or more wavelength convertersperforming any demodulation of, and without the one or more wavelengthconverters performing any modulation of, the one or more optical signalsthat are provided to the one or more optical networks that are externalto the ground based optical gateway.
 24. The ground based subsystem ofclaim 15, further comprising: one or more frequency converters each ofwhich is configured to one of up-convert or down-convert a frequency ofat least one of the one or more optical signals, that is being providedto one of the one or more optical networks that are external to theground based optical gateway, before the one of the one or more opticalsignals is provided to the one of the one or more optical networks thatare external to the ground based optical gateway, without the one ormore frequency converters performing any demodulation of, and withoutthe one or more frequency converters performing any modulation of, theone or more optical signals that are provided to the one or more opticalnetworks that are external to the ground based optical gateway.
 25. Theground based subsystem of claim 13, further comprising: a plurality ofphotodetectors, each of which converts a different one of a subset ofthe optical signals that are output from the WDM demultiplexer, to arespective electrical signal.
 26. The method of claim 18, furthercomprising: converting at least a subset of the optical signals thatresult from the demultiplexing to respective electrical signals.